Grammar Bi vs. Semi (weekly, monthly, annually) |
The Blue Book of Grammar and Punctuation

Bi vs. Semi (weekly, monthly, annually)

Using bi or semi in front of time periods can create tremendous confusion these days as definitions and style guidance continue to soften and blur.

To illustrate this, we located the following definitions of words with the bi or semi prefix after researching both style books and dictionaries.

Biweekly: once every two weeks or twice a week
Bimonthly: once every two months or twice a month

In addition, a biweekly publication is issued every two weeks and a bimonthly publication is issued every two months.

Then we have this from The Associated Press Stylebook:

Biannual: twice a year, synonymous with semiannual; for “every two years,” use biennial.

Consider these definitions as well:

Semiweekly: twice a week
Semimonthly: twice a month

Those of us who resolutely uphold precision might cling to Latin’s original intent for bi and semi: bi = two, semi = half (or twice). Such loyalty to Latin would give us biweekly for “every two weeks” and semiweekly for “twice a week.”

Conversely, those of us who note that the blurring of bi and semi will only get greater will avoid confusion altogether by stating the actual time frame. Instead of battle with biweekly or semiweekly, we will say “every two weeks.” Rather than wrestle with bimonthly or semimonthly, we will write “twice a month.”

If the article or the existing discussions do not address a thought or question you have on the subject, please use the "Comment" box at the bottom of this page.

147 responses to “Bi vs. Semi (weekly, monthly, annually)”

  1. mike says:

    how can this be accurate?!?!?!:
    Biweekly means once every two weeks or twice a week.
    Bimonthly means once every two months or twice a month.

    It seems to me that this confusion is perpetuated by “authorities” who have accepted the generally misunderstood use of the words. This definition below actually has some merit and should be taught by all:

    The English prefixes bi- and semi- are often mixed up by native speakers. A semi-annual reading of this lesson will help more than a bi-annual one.


    Bi- comes from the Latin meaning two. When used with a temporal word, bi- means “every two” or “every other.”

    This magazine is published bi-weekly, on the 1st and 15th of the month.

    Congressional elections are held biennially, on even-numbered years.

    The U.S. celebrated the bicentennial of its 1776 founding in 1976.


    Semi- comes from the Latin meaning half. When used with a temporal word, semi- means “twice.”

    Our semi-annual meetings are in January and July.

    I get paid semi-monthly, on the 5th and 19th of each month.

    The semi-weekly deliveries occur on Monday and Thursday.

    The Bottom Line

    The confusion between bi- and semi- occurs because both prefixes are related to the concept of two. But bi- means something that happens every other (week, month…), or every two (weeks, months…), while semi- indicates something that happens twice every (week, month) or every half (week, month).

    • Jane says:

      I agree with you wholeheartedly that the distinctions between “semi” and “bi” should be kept; however, because people confuse the two, the language has evolved (devolved) such that these prefixes are now often synonymous. By the way, you presented a very well-written argument!

      • Joe says:

        Apparently “evolved” and “devolved” are now also interchangeable as well…

        • Anona says:

          Evolve vs devolve…

          Both refer to evolution, however devolve refers to a downward evolution… thus devolve is a subset of evolve. Evolve is not necessarily an upward evolution.

          • says:

            We assume that Joe was being sarcastic.

          • Mark Harder says:

            Evolution of grammar is always to be expected. Some changes are trivial (“pleaded” now instead of “pled”). Others are offensive to value systems. The confusion between bi- and semi- periodic could cause a potentially serious lapse in communication if, for example, one were to expect arrival on Thursday of an item that won’t be delivered until the week after next.

          • Greg says:

            Evolution only works in one direction, evolution will only take something back to an earlier state if changed conditions make that early state better adapted to changed conditions making it the now more evolved state.

            Devolve is merely evolve rebadged; rebadged under the bias of believing you the observer can see the true way forward.

            It’s all comes down to perspective and bias: Is the moon to the left or the right? Left you say. You’re wrong just turn around and you’ll it’s on the right. In truth though it cannot be defined as being either the left or the right; it’s in the east on the horizon. But still we’re wrong, move half way around the earth and it’s on the western horizon…..

            The take home message is: there is no such thing as devolving, except where politicians are concerned.

    • Jim says:

      Good explanation except for one thing… You say “This magazine is published bi-weekly, on the 1st and 15th of the month” That’s not entirely accurate and would be better to say that it occurs semi-monthly, i.e., twice a month on the first and 15th.

      If it were truly published bi-weekly, on the 1st and 15th, then the next publish date should be the 29th, 2 weeks after the 15th. That of course would throw off the next publish date of the 1st…

      • cooganalaska says:

        Semi-monthly would mean 24 publications per year while bi-weekly would mean 26 per year. These two terms are not synonymous.

    • leigh says:

      I think you are saying the same thing as the original post. Please correct me if I’m wrong
      “Biweekly means once every two weeks or twice a week.
      Bimonthly means once every two months or twice a month…
      Semiweekly means twice a week.
      Semimonthly means twice a month.”

      Your argument:
      “Bi- comes from the Latin meaning two. When used with a temporal word, bi- means ‘every two’ or ‘every other.’…Semi- comes from the Latin meaning half. When used with a temporal word, semi- means ‘twice.'”

    • JDave says:

      Mike said: Bi comes from the latin word meaning two.”

      If you revert to the Latin, then Mike may have a change of heart.

      “Bi” actually comes from the Latin word “Bis” which translates to TWICE. “Duobus” or “Duo” is the Latin for two. Biweekly would mean twice-a-week. To answer Mike’s question, that’s exactly why bimonthly can mean two things. People began to use it wrong (saying that biweeky means every other week), and it stuck for some. That’s the language. It changes over time. That’s why there is really only one rule:

      If you want to be clear in your communication, stop using “bi” words. Use “every other…” or “twice a…”.

    • DaveJ says:

      If a semi-circle is 2 parts to the circle, then semi-annually should mean 2 times per year. (ex: Jan/Jul)
      If bicycle means 2 wheels, then bi-annually should mean every 2 years.

    • Jason says:

      Ironically, in your attempt to assert the correct usage of bi-weekly, you have made a mistake. A publication that is published on the 1st and 15th is semi-monthly, not bi-weekly. The difference is that a semi-monthly publication is published 24 times in a year. A bi-weekly publication is published 26 times in a year, or 27 times if the first one is published on January 1st, or on January 2nd in a leap year.
      Thank you.

  2. a reader says:

    The original post is wrong and has just confused any reader.

    Biweekly DOES NOT MEAN twice a week. Twice a week is SEMI-WEEKLY.

    BI = every two
    –Bi-weekly = evey two weeks
    –Bi-monthly = every two months
    –Bi-yearly [Bi-annually] = every two years

    Semi = half
    –Semi-monthly = twice per month (roughly every two weeks in perspective to a month, meaning it is not exactly 14 days)
    –Semi-yearly [Semi-annually] = twice per year (every 6 months)

    • Jane says:

      The prefix “bi-” has taken on both meanings: every two and twice. Therefore, one must now EXPLAIN oneself when writing or saying an expression such as “bi-weekly.” Please don’t blame the messenger (me) for this unfortunate development.

      • Jim says:

        I have to disagree with you. Just because many people use these words incorrectly, doesn’t mean that their definitions have changed. I think that a website or blog such as this should clearly articulate what is correct and incorrect, and not add to the confusion by saying both are correct. As an arbiter for proper use of the English language, this website should be steadfast in sticking with the definitions and proper word usage.

        • says:

          Like it or not, the prefix “bi-” has taken on both meanings: every two and twice. Languages evolve over time; rules governing grammar and punctuation change. Therefore, one must now be very specific when writing or saying an expression such as “bi-weekly.” Even though we agree with you that the distinctions between “semi” and “bi” should be kept, the purpose of this website is to interpret and reflect the rules of English grammar and punctuation as adopted by the leading authoritative resources such as The Chicago Manual of Style, The Associated Press Stylebook, and others.

          • Chris says:

            Finding this discussion quite interesting after a meeting at work was scheduled bi-weekly causing confusion. Your comments around accepting the fact that language has devolved concerns me as well some others. Does this imply that we must also accept the use of the phrase “mute point” over “moot point”? I hear many many people using “mute point” and it disturbs me greatly, though I have yet to correct anyone.

            • says:

              Mute point is certainly incorrect. Pointing it out to someone during a conversation is up to you.

        • Donna says:

          I totally agree with you, Jim. Teach it correctly, don’t “devolve” just because people can’t remember the correct way. I used a trick to remember: Bi-weekly paycheck means you go BY one week without getting a check. You get your check every other week (26 bi-weekly pay periods in a year). Semi-monthly paycheck — think of getting hit by a semi: bump, bump! You get paid twice a month. 24 pay periods in a year.

          • says:

            We are not encouraging anyone to “devolve” the language. We are simply pointing out the fact that these are words that are often confused because the language has changed over time. Check your dictionary to see what these words mean.

          • David says:

            The way I remember which usage is correct (and I do believe there IS a “correct” way to use these terms, common errors notwithstanding) is to remember that a bicentennial is celebrated as the 200th anniversary of an event not twice in a century. That helps me know that two centuries have elapsed and lets me know that bi-anything describes intervals of two units. That leaves semi-anything to mean intervals of one-half units. It isn’t that hard if it matters. That is the problem though; it doesn’t matter to enough people and the people for whom it does matter are seen as odd, compulsive or arrogant. That’s too bad. Appropriate grammar is now excessive.

        • Greg says:

          But Jim, while I agree with you 100%, it’s unfortunate to see “The American Heritage Dictionary” print that “non-standard English grammar” can have “bi-weekly” mean “twice a week”, while “standard English” will mean every two months. What are we doing to our language? I agree with you that non-standard usage should not become O.K., acceptable or correct just because people can’t get it straight. We just lower the bar and the quality of definition, and language. I’d love to hear from an English teacher. Do they question this stuff? I thought one reason we had dictionaries was to clarify the meaning of words. Okay, I gotta go get a life now. Later!

  3. greg says:

    if the messenger is knowingly delivering a bad message, then i shall blame the messenger. i suppose you would write that it is OK to to place “an” in front of the word “historic” because it’s starting to become common (devolve) to make the “h” silent. (bob costas says it that way!)

    • Jane says:

      I would not write or say “an historic” because the “h” is still audible.

      • Bob says:

        “An historic….” is correct in England. I suspect “A historic…” is probably correct in America. The same goes for the arguments about bi- and semi-, which may also differ in meaning on either side of the pond. Another interesting example is “Momentarily”. If I use it, I mean “For a moment”, whereas if my American friends use it they mean “In a moment”. So, “I will be with you momentarily” in the US is “if you wait a very short time I will be with you”. In England “I’m with you now but I’ve got to go.”

        • says:

          Yes, this site represents American English rules and guidelines. You’re correct about the American meaning of momentarily. That’s interesting to hear how it differs from its use in England.

        • Suzanne says:

          “An historic” is also correct on this side of the pond. Unfortunately, most people in the US do not generally understand the definition of “in a fortnight” (meaning once every two weeks, or bi-weekly). That would be a great solution to the problem. However there is a difference when discussing usage vs. definition. Such as when discussing “momentarily”. I think you are, correctly, pointing out the difference in the usage of the word in the US vs. Britain, not the definition. Albeit an interesting one! Just as in the first post, the writer used pay periods as an example, which does cause confusion and, as an employer I find that I need to clarify way more often than I should… to the point that it has become part of my standard speech to new employees. And I think the discussion “devolved” from there. Sadly, people have become very accepting of those who think it is ok to have a lower standard of English grammar. Certainly on this side of the pond! Just one more thing for people to make fun of us for, lol!

          • says:

            You bring up an interesting point regarding usage vs. definition. According to Merriam-Webster online, momentarily can be defined as either “for a moment” or “in a moment.” We Americans use the latter definition while the former is the usage in Britain.

            We are unclear about whether you are saying in your first sentence that an historic is correct on both sides of the pond. We want to reiterate that a historic is correct in American usage.

  4. That Dude says:

    Don’t shoot the messenger. Mike got it right. Take his justification as a basic grammer reminder to the folks at Webster and start righting the wrong.
    Having a secondary meaning for a term evolve through usage is one thing. Having a contrary meaning is simply wrong. Standard bearers are supposed to guard against that.

  5. John says:

    Putting aside the rants, the following is a contradiction and cannot be accurate, regardless of the word used:

    “Biweekly means once every two weeks or twice a week.”

    The same goes for Bimonthly.

    If it’s “once every two weeks”, that’s equal to twice every FOUR weeks, not every week. Jane, I’m still confused. I think you should correct this post.

    • says:

      Every dictionary we have checked agrees with those definitions. “Biweekly” and “bimonthly” both have two distinctly different definitions, so we can understand why you are confused. If you ever subscribe to a biweekly or bimonthly publication, you will need to make sure you understand the terms.

  6. Candy says:

    I guess the main purpose of language is clear communication – picking the shortest way of writing or saying something isn’t always the best option.
    It doesn’t take a massive amount of either breath or keystrokes to use
    “twice yearly” or “every two years” instead of either “semi-” or “bi-” leaving no further clarification necessary. Job done…

    • says:

      We agree that the shortest way is not always the best. If a little extra effort makes things clearer for the reader, it’s worth it.

  7. Fran says:

    What I don’t understand is the dictionary defines ‘bi-annual’ as twice a year.

    • says:

      Unfortunately, this is another example of how the language has evolved (or devolved). Some dictionaries list only the one definition, however lists two different definitions for the word biannual:

      1. occurring twice a year (semiannual) and
      2. occurring every two years (biennial)

      That’s why we recommend using the actual time frames to avoid confusion. For example:
      Teresa visits her parents in Manila twice each year.
      Teresa visits her parents in Manila once every two years.

  8. Sebastian says:

    I’m not sure why the examples given equate bi-weekly and semi-monthly- they are not the same thing.

    For example, most people get paid bi-weekly (that is, 26 paychecks a year) but my company pays me semi-monthly (24 paychecks a year). One isn’t better than the other, but I’m VERY aware of the difference. Personally I prefer semi-monthly paychecks; bills, rent, etc are all monthly expenses, and the bi-weekly schedule for paychecks ensure they often don’t match up with incoming expenses.

    • says:

      The examples equated biweekly and semimonthly because that is how they are defined in the dictionary. “Bi” and “semi” are now often synonymous. You gave some good examples of why it is so important to understand the exact terms when either of these words is being used.

  9. Andy says:

    I like Fortnightly…only one meaning

    • says:

      And for our American readers, fortnightly means occurring once in a fortnight (14 days).

  10. Nick says:

    I use bi-weekly and bi-monthly in the same way as bifurcate – to split in two.

    • says:

      We suppose you have about a 50% chance of being understood! (By the way, neither biweekly nor bimonthly is hyphenated.)

      • Mark says:

        Don’t you mean “Semi-change” (sorry had to say it)

        • Nick says:

          Mark – I’m sorry, but you meant semi-chance. Nothing worse than getting the grammar wrong in a sarcastic reply to someone correcting another person’s grammar.

          • Tom says:

            Picking on a typo and calling it a grammar error, instead of pointing out one of the genuine grammar errors, in your post pointing out the the irony of getting the grammar wrong in a sarcastic reply to someone correcting another person’s grammar might, in fact, be worse than getting the grammar wrong in a sarcastic reply to someone correcting another person’s grammar. Neither, however, is worse than taking the trouble to look for grammar errors in the previous ridiculous sentence and then realizing that that’s how you just spent your valuable time.

          • Charles says:

            Writing a double “the” as in “pointing out the the irony” when criticizing someone’s picking on a typo and calling it a grammar error in a sarcastic reply to someone correcting another person’s grammar is a special kind of irony.

  11. Mike says:

    Nick, I think you’re pointing to the source of the confusion. Many people think that since bifurcating (or bisecting) something divides it, then biweekly must mean to divide the week; but they misunderstand the derivation of the word. The reason that bifurcating something divides it is because it causes it to have two (bi-) forks (furcates) or branches. (Bisecting creates two sections). Over time this confusion has become so widespread that the words biweekly, bimonthly, etc., have lost their utility. I agree that dictionaries should seek to guard against this, but word misuse isn’t illegal, much as we might lament it.

    Shall we talk about the similar state of the word “peruse” next?

    • K.W. says:

      It is interesting to note, from a historical viewpoint, the original meanings of either twice a week or every two weeks emerged around the same time – 1865, although the meaning of twice a week is believed to predate every two weeks.

      This may be due to the fact that biannual emerged around 1837 meaning twice a year.

      So this is not a new confusion of terms, but based in history. We may be evolving the language to two different prefixes to avoid confusion. However, we are not contributing to an erroneous usage when we use the prefix ‘bi’ to mean twice in a time period.

  12. Matt Emerson says:

    The confusion is easy to explain if you think of it in terms of period and frequency and ambiguous association of the word parts.

    Breaking down the term biweekly, for example:

    bi: 2,
    week: a period of one week,
    ly: converts a period to a frequency, or “once per”. This is the equivalent of taking the inverse (1/X) in mathematics.

    So translating to mathematics ambiguously gives:
    1 / (2 * week) or 2 * (1 / week)
    where what goes in or out of the parentheses isn’t clear from the word.

    Back to words, these correspond to associating the parts like this:
    (biweek)ly or bi(weekly)
    with the the parentheses in either of two positions.

    This analysis applies to all the periods (week, month, year) the same way. It also applies analogously for the “semi” prefix and for the less common “tri” prefix and other numeric multiplier prefixes.

    Neither seems obviously better to me, but noting this usage: “Our semiannual meeting (without the “ly”) is held semiannually” implies to me that the whole front part of the word is the repeating period, so the first way of associating the word parts seems a little more consistent.

    This would make the (semiannual)ly association the preferred one, and it would mean once every half year, or twice per year. This would also make biannual consistent with biennial, and it produces the usual association for fortnightly, for whatever that’s worth.

    Someone noted that these words are not hyphenated. I could see where hyphenating them might indicate the alternate association, but of course that assumes you know what the usual association is!

    • says:

      We’re glad you found this easy to explain, Matt. However, we hope no one receives a letter or email explaining that the semiannual meeting is held semiannually!

  13. Karl says:

    I love Mike’s definition above. However, the example for bi-weekly given (“This magazine is published bi-weekly, on the 1st and 15th of the month.”) is I think incorrect. Because weeks are of fixed length and months are not, bi-weekly (ie. every two week) publications can’t possibly fall on the 1st and 15th of every month. Semi-monthly should have been applied in this instance. This highlights the subtle difference between the bi- and semi- prefix when applied to a temporal word. If your employer tells you that you get paid semi-monthly (ie. 1st and 15th) and you take that to mean bi-weekly and set your auto billpay for every other Friday, you’ll be bouncing checks on most months! Bi- simply means “two fixed periods added together”; semi means “happening twice in a fixed period”. Semi- can always mean bi- but bi- may not necessarily imply semi-. I love to add to the confusion.

  14. MarkG says:

    This whole thread of responses gives a debate about the evolving usage of these words. It has been politely and professionally enjoined by all of the participants, which speaks well of all of you. I especially like Matt Emerson’s discussion of how the ambiguity that seems to have arisen in these words can be represented as an ambiguity in the order of mathematical operations.

    I’m not sure if anyone has established with research that the terms used to be clear and are only recently becoming confused. But that has been alluded to in the thread. So, if that is correct, then we are seeing some evolving language use at an interesting time in its development.

    I’m not a linguist, but I have known a few. They study, among many language phenomena, how word meanings change over time. Because in the end, one can see that word and phrase usage is a community convention. And I believe there are some examples where those in authority positions on language usage have tried valiantly, but failed to stop an incorrect usage from arising, becoming common, and finally becoming accepted. If someone has any good examples of this, I’d love to hear of them. The only one I can quote is the use of the word “hopefully”.

    So, is it too late to stop these prefixes from becoming confusing? Can the English teachers and makers of dictionaries and people who publish style manuals across the land make a campaign to assert their authority and make sure that it returns to a clear case:

    bi-Xly meaning once every 2X’s
    semi-Xly meaning twice every X

    I can imagine a social experiment with enough interest in which they could actually win the day.

    But then the problem is that people use words quickly and with only slight effort to choose correctly, so there will always be the pressure for the confusion to arise again. After a whole generation attests to the shining success of our grammarians in helping clarify the use of our entire language community, I assume the confusion would begin again to slowly creep in.

    On the other hand, perhaps a concerted effort could be mounted again as often as necessary. I don’t believe that all gardens ultimately will succumb to the jungle, because they can be maintained indefinitely with a steady effort.

    Sorry for the length of this post (if it gets accepted). I just couldn’t resist putting all of these thoughts down once.

  15. Jeff says:

    There is plenty of comment on the fact that the English language has evolved/devolved and it seems to be the justification for incorrect usage of words and/or prefixes. I believe that rather than teach that “both are now accepted,” we should teach that “although both are being used interchangeably, X means P and Y means Q” (not X means P and/or Q, as does Y).

    If we keep accepting change based on ignorance, we’ll soon be reading books written in “leetspeak” and/or “SMS language.”

    I w0u1d h8 that!

    • says:

      Our practice is to inform our readers as to what is currently considered acceptable and let them decide for themselves if there are multiple options. Quite often it will depend on the context and the situation. We do not “justify” anything that is “incorrect usage.”

  16. Troy says:

    > If you mean every two weeks,
    > you may also say, “I visit my aunt semimonthly.”

    Being paid every two weeks is much different than being paid semimonthly. There will be some months where I’m paid three times in a month.

    • says:

      As stated earlier by Sebastian, his company does pay semimonthly (24 paychecks a year). Your company pays biweekly. To avoid confusion, you may want to substitute the actual time frame for these terms.

  17. Charlie Hand says:

    Here’s how I get confused. I know what weekly is (once a week). I know what bi means (2) and I know what semi means (1/2). The reason I pause is: does the prefix apply to the frequency of the events or to the period of the events? Semiweekly: Half of the frequency “once a week” is once every two weeks, whereas half the period “once a week” is twice a week. The correct answer of course is, semi refers to half the period, not half the frequency. But it cannot be deduced. It has to be memorized.

    • David says:

      You need not just “memorize” it. Just remember one that you would never misuse, such as my favorite, a bicentennial. Nobody would ever confuse that one and say a bicentennial should be celebrated twice per century. That clarifies that “bi” means an interval of two units, whatever they are weeks, months, years, etc.). That leaves “semi” to mean intervals of one-half units, or twice per unit. By the way, there are some terms for which it really does matter. Try making the incorrect substitution for terms like bipedal (?semipedal), bicycle (?semicycle), or bipolar (?semipolar). Using the possibility of equivalence would mean we could walk on half a leg, ride on a device with one half of a wheel, or have someone be mentally ill with one-half of a mental state instead of two diametric ones. Sometimes flexibility is OK; sometimes, it’s not.

  18. Julie says:

    If I get paid semi monthly, should my pay checks be more for the months that have three paychecks in it? Right now it`s the same no matter how many weeks there is in that month and i feel like I am working a week for free.

    • says:

      Semimonthly means twice a month. That means you get 24 paychecks a year. A person who gets paid biweekly (every two weeks) gets 26 paychecks a year. If a worker is earning a known annual salary, then it all comes out the same whether it is divided by 24 and paid semimonthly or whether it is divided by 26 and paid biweekly.

  19. erich says:

    I don’t think words have devolved, I think people, specifically our literacy and attention to detail have devolved. Factor in an increase in cultural diversity and we have a society where a growing majority misuse words and, over time, redefine the English language. I’m 43 years old. If I tried to sell bi-weekly as twice a week (semi-weekly) when I was in elementary/middle school 30-35 years ago, I’d currently be the oldest 5th grader on the planet. At the current rate, in another 30-35 years, bi-weekly may mean a few times a week, every several weeks or anything in between. Fabulous.

    Wait, I have an idea. Use semi-weekly – since it doesn’t (currently) have conflicting definitions – to convey twice a week and use bi-weekly for every two weeks(as originally intended).

    Of course, to avoid ambiguity, one could go with semi-quad-weekly (twice every four weeks). Just saying.

    • Don says:

      I agree. It is a sad thing. I often find myself envisioning a pile of hacked off antlers when I hear the way asked and else are pronounced. Did they miss grade school?

  20. Sallia says:

    Eric and Jane have excellent points at the top of this post. You should visit your aunt more often.

  21. Kieron says:

    MarkG – I have one for you… Professional
    My English teacher always used to lament its misuse.
    A professional is someone who does something for reward
    NOT someone who does something well (He argued)
    I loved my English teacher’s passion for language.
    Sorry Mr MacGregor, I let you down Sir.

    Couldn’t we use Demi-weekly?

  22. Erik says:

    What is the significance of the dates beneath Jane Straus’s photo?
    Did Jane Straus pass away on February 25, 2011?
    If so…

    • says:

      We’re afraid so, Erik. From the “About Jane” tab on the website:
      “As we first announced in our weekly E-Newsletter of March 8, 2011, we are deeply sorry to inform all of our loyal readers and fans that Jane Straus passed away on February 25, 2011. For two years Jane waged a heroic battle with brain cancer. Unfortunately, medical science only has treatments but no cure for this disease. That did not deter Jane, though, from continuing to be fully dedicated to her family, friends, and her readership right up until the end.

      Jane wanted The Blue Book of Grammar and Punctuation and the website to survive and flourish in order to serve anyone and everyone seeking to improve English grammar and punctuation skills. Lester Kaufman, her husband of 23 years, along with the skilled staff of our web master, Weblinx Inc., will ensure that Jane’s legacy lives on.”

      We have taken on her mission of offering this free resource, keeping it updated, issuing weekly E-Newsletters, and responding to readers’ questions.

  23. Jon C. says:

    In your definition of this it says these cause tremendous confusion and I was even more confused when you said that bi-monthly is every other month and twice a month. How can it be both?

    • says:

      As stated in the Chicago Manual of Style, bi generally means “two” and thus bimonthly would indicate every two months, while semi means “half” and thus semimonthly means “twice a month.” Unfortunately, these prefixes are commonly confused. And this is not even a recent development. Whether you look up bimonthly on or in a 1973 copy of Webster’s New Collegiate Dictionary like I have on my bookshelf, you’ll find bimonthly defined as both “occurring every two months” and “occurring twice a month.” At least semimonthly has remained steady at “occurring twice a month.” To avoid being misunderstood, be explicit, e.g., “The magazine is issued once every two months” or “The magazine is issued twice a month.”

      • Dan says:

        As stated in the Chicago Manual of Style, bi generally means “two” and thus bimonthly would indicate every two months, while semi means “half” and thus semimonthly means “twice a month.”

        Clarity can be increased even further by stating it this way:

        As stated in the Chicago Manual of Style, bi generally means “two” and thus bimonthly would indicate every two months, while semi means “half” and thus semimonthly means every half month.

        • says:

          “Half month” is an unusual term in American English. We are not convinced that it is any more clear than “twice a month.”

  24. Emily says:

    Can I say semi-biannual to mean twice every two times a year, so four times a year?

    • Emily says:

      Or is there another way to say four times a year without saying “quarterly”.

      • says:

        As we stated in our Bi vs. Semi (weekly/monthly/annually) blog, the terms semiannual and biannual can cause tremendous confusion. Combining the two would just add to the confusion. The word quarterly is clear and uncomplicated.

      • Tom says:

        semi-biannual would be terrible and unnecessarily confusing way to express annual

        • Tom says:

          not quarterly.

          • says:

            Even though it may be amusing to play with odd terms like “semi-biannual,” it reinforces how confusing it has become to use the prefix bi. Since “biannual” may mean either twice per year or every two years, “semi-biannual” (a term nobody should use) may mean either quarterly or annually. Obviously, it’s better to use unambiguous terms that leave no doubt about what you mean.

  25. Cindy Blackburn says:

    Someone please explain this…Company A pays bi-weekly. I want to purchase health insurance through them. My options costs of $87.18 or semi-monthly of $94.45. Why is there a difference in price?

    • says:

      The word biweekly has been so carelessly used over the decades that it now means both “every two weeks” and “twice a week.” In this specific case, if you are paying biweekly, you are making 26 payments each year (a payment every two weeks). Paying semimonthly means you are making 24 payments each year (two payments each month).

  26. Jessaca says:

    My DD brought home her 4th grade spelling with the word biannual meaning twice a year but biweekly and bimonthly as meaning every 2 weeks or months, respectively.

    • says:

      That’s why we devoted this blog to this unfortunate subject. It seems even the teachers are confused by it.

  27. DJ says:

    Biweekly is not the same as semi monthly. Although they are close in timeframe they don’t technically equal each other. If I get paid biweekly, I will receive 26 paychecks in a year. If I get paid semimonthly, I will get receive 24 weeks a year. Although it is a small difference, it is a difference.

    • says:

      The examples in the blog equated biweekly and semimonthly because that is how they are defined in the dictionary. “Bi” and “semi” are now often synonymous. Your example shows why it is so important to understand the exact terms when either of these words is being used.

      • Beorn says:

        In many countries – notably Costa Rica and Nicaragua – workers are paid semimonthly, 24 equal paychecks per year. Everyone then receives a full months pay as a government-mandated bonus at the end of the year. So the end result was that they were paid for 26 weeks, the proper number of weeks in a year.

        The workers I knew when I lived there were not confused, saw the bonus as the employer giving them the biweekly pay that was due for their daily toil.

  28. Mark Harder says:

    Evolution of grammar is always to be expected. Some changes are trivial (“pleaded” now instead of “pled”). Others are offensive to value systems. The increasingly frequent use of “that” as the beginning of adjectival phrases referring to people (people “who”) as objects. The usage of “that” applied to people almost always stands out from the written page, an ugly unwanted interruption in my reading, to say the least.
    The confusion between bi- and semi- periodic could cause a potentially serious lapse in communication if, for example, one were to expect arrival on Thursday of an item that won’t be delivered until the week after next.

  29. Lerato Lenka says:

    How do I prepare a bimonthly schedule for a soccer tournament. I need an example in form of spreadsheed or tell me how do i go about doing the schedule

    • says:

      As our blog states, bimonthly can mean “once every two months” or “twice a month.” We assume that the schedule for a tournament would be twice a month, but you should confirm with the person making the request. Preparing spreadsheets is beyond the scope of our blog.

  30. Roy says:

    Bi- means two and semi- means half. An accepted mis-usage is still wrong. The prefix bi- has a fixed meaning and the prefix semi- has a fixed meaning and authorities are sometimes wrong. Bi-monthly has only one correct definition and that is every two months. The interpretation of bi-monthly as twice per month might be officially accepted but it is still wrong. Since 2 never equals 1/2, then bi-monthly can never (correctly) have the same meaning as semi-monthly.

    • says:

      As we have responded to a number of previous posts, our job is to inform our readers about dictionary definitions and interpret and reflect the grammar rules. Our blog does not encourage incorrect usage. We are simply pointing out that these words are often confused because the language has changed over time.

  31. Sue says:

    Wow, I just want to commend everyone for the lively discussion. I just googled “biweekly” for the correct usage of the term and realize I could spend my whole morning studying the arguments. I have to admit I did get quite a few chuckles out of this, as well. (And yes, I do work for a living) I’m going with “every other week”, but feel compelled to define myself when using the term; which, I guess, makes no sense to use the term in the first place.

  32. Nancy says:

    Good Lord. A 6 year discussion on this subject?

    It was, however, quite entertaining and a good way to waste a few minutes. Unfortunately, I’m still confused on the usage. In the email I was writing, I changed biweekly to every other week because obviously everyone has a different interpretation of the word.

    I do agree with the person who posted “bi-Xly meaning once every 2X’s, and semi-Xly meaning twice every X”. Easy rule to follow and I’ve posted it at my desk for everyone to see. Until I can retrain everyone who reads my emails or speaks with me to understand the difference, though, I will not be able to use the prefix bi or semi. *sigh*

  33. Jennifer Meacham says:

    I disagree from this standpoint:

    Bi means two. If the barometer is “weekly,” then bi-weekly would seem to mean you’re meeting two times or twice each week.

    Semi means half, partially or incompletely. Again with a “weekly” barometer, if you’re meeting half as frequently as weekly (not MORE frequently than weekly) then you would be meeting every other week. You’re only partly meeting once a week, at every second week instead.

    That being said. I can see the trouble. If Bi means two, then wouldn’t that mean two weeks are needed to create something that’s “bi-weekly”? Then semi could mean “half of a week.” Uggg. I’ll stick with “every other” or “twice a week”….

    • says:

      We do not know who or what you disagree with, unless it is the dictionary. As our blog states, we also “see trouble.” That is why this blog was created, to point out the possibility of confusion with these terms. We do not advocate any particular way of using these terms, but we do suggest substituting actual time frames to avoid confusion.

  34. Mark says:

    Why would you say biweekly for once every two weeks? Have you not heard of the word fortnightly? It removes any confusion.

  35. Patrick Adams says:

    Why CAN’T there be a definitive definition, so there is NO confusion.
    if Bi means 2, than bi-weeky should mean every 2 weeks and bi-monthly should mean every 2 months
    Accordingly if Semi means Half, than semi-monthly should mean twice per month.
    Also, what is the word for the period of every 4 months.. tertiary?
    This is like the futile discussions with people about ‘this week’ and ‘next week’, especially if you’re using these terms on a friday.
    thanks, Pat

    • says:

      We do not advocate any particular way of using these terms, but we do suggest substituting actual time frames to avoid confusion.

  36. Andy says:

    Would that be semi or bihourly?

  37. James McFadyen says:

    It may not work for every situation but my aide memoir helps me (in most cases):
    If I were bilingual, would I be fluent in 2 languages or fluent in half a language?

    • Snarky Snarkenheimer says:

      If you are American and partially learned another language, you would probably be semi lingual as my experience on Facebook has taught me that my fellow Americans have a ghastly knowledge of the English language.

  38. Krom God of Steel says:

    It seems to me that the confusion occurs because it is not clearly stated to which half of the equation the prefix refers. Given that the equation is occurrences per time period, if “bi” refers to occurrences, that is two occurrences per time period. If “bi” refers to time periods, then it is one occurrence per two time periods.

    “Semi” is a bit more abstract, since it means “half”. So since the OP stated that “semi means twice a week”, we accept that it always refers to the time period, so the initial equation is 1 occurrence per half a time period, which seems more naturally expressed without any fractions, so we say two occurrences per time period.

    IMHO, if we accept that “semi” will always refer to the time period, then we should be consistent and also use “bi” to always refer to the time period. So “biweekly” would always be once every two weeks.

  39. G-man says:

    It would mean your linguistic capabilities are divided between two languages.

    The most accurate latin meaning of bi is being composed of two parts or units.

    Bi certainly does not mean “two.”

    That is the Truth.

    • says:

      The dictionary definition of the English word bilingual is “able to speak and understand two languages.”

  40. Michael Steffen says:

    I agree with Mike in his circa 2009 posts. I agree also that when dictionaries fail to maintian sanity about the use and meaning of words that it is the responsibility of those of us who still care to not just parrot what the dictionary may say but also acknowledge that the dictionary(s) have failed us and to give the sort of thoughtful and clear understanding that was given by Mike. Just bowing to the dictionaries and re-iterating their failings as did in the first post of July 29 2008, is a travesty. We, as those concerned with clear precise and unambigous communications, have a responsibility to encourage the better use of the language even in the face of a dictionary that embraces the devolution of that language. An evolving language can be a good thing, I agree with and understand that. But there is NOTHING GOOD about a language in which a sufficient volume of mis-use results in something being deemed correct, especially when that new acceptance condones and facilitates mis-communication. Grammar is base in rules and commmon understanding. Those rules should not change on the whim of the ignorant; nor should they change based on a wide spread usage that leads to the errosion of clear communications. “Authorities” like need to help hold dictionaries to a higher standard than they seem to be willing to hold themselves.

    • says:

      Apparently, you missed our reply of July 17, 2009, to the comment submitted by Mike, in which we agreed with him wholeheartedly. If you read through some of the earlier posts in this blog, you will note that our website is simply explaining definitions, reporting current usages, and interpreting and reflecting the rules of English grammar and punctuation. We prefer to explain dictionary definitions rather than chastise them. To call our approach a “travesty” is a bit extreme. After misspelling words such as maintain, common, based, and erosion; using all caps and run-on sentences; and inserting unnecessary hyphens in the words misuse, reiterate, and miscommunication; we question your “authority” to be using quotes around the word “Authorities.”

  41. Reader Writer says:

    Your response is confusing. I can’t determine if you’re bi-wrong or semi-wrong. Using GrammarBook as a source for Grammar and Punctuation might get your gramma mad and your editor punchy. At least you began with a true premise. (And you got me to look up “doublespeak”).
    My grammar just wouldn’t be the same without you!

    Your words:
    “Using bi or semi in front of time periods can cause tremendous confusion.
    > Biweekly means once every two weeks or twice a week.
    Bimonthly means once every two months or twice a month.”
    Yes, it doesn’t.

    • says:

      Our article is intended to point out that decades of careless usage have made these terms ambiguous. The meanings cited are dictionary definitions.

  42. Bennett says:

    In searching the difference between bi- and semi-, your website leads off with :

    Biweekly means once every two weeks or twice a week.
    Bimonthly means once every two months or twice a month.

    If something is “once every two weeks” as noted above, then it is twice a month (not twice a week).
    And, if something Bimonthly is “once every two months” it does not mean twice a month.

    In clarifying the difference, you confused.
    I don’t know how people blogged and didn’t catch this.

    Please correct.

    • says:

      Unfortunately, it appears that you misunderstood the article. There is nothing to correct. The meanings quoted are dictionary definitions. If you read through some of the comments, you will see that people clearly caught on. You will also see that we are just as upset about this situation as everyone else. We are advising our readers of this oddity, and we offer a way to avoid confusion.

  43. Michael says:

    Biweekly means once every two weeks or twice a week.
    Bimonthly means once every two months or twice a month.
    Doesn’t anyone else see the contradictions in these two statements?
    “Biweekly means once every two weeks or twice a week.” Well, which is it? Every two weeks or twice a week?
    “Bimonthly means once every two months or twice a month.” Well, which is it? Every two months or twice a month. Pick one, you can’t have both and be correct?

    • says:

      Yes, that’s the point of our article. We see the contradictions and have acknowledged them in the blog. That is why we said that to avoid confusion, you may want to substitute the actual time frame for these confusing terms.

  44. Skip says:

    It’s unfortunate the bi- words discussed above have lost concrete meanings. Their dual meanings most certainly cause much confusion. Maybe through the following explanation, someone on this page can solidify their use of at least the prefix bi- in their communications.

    Bisect is a verb meaning to divide something into two equal parts. Sect, to cut, looks to bi- to determine how many parts should be the result, not how many times the cutting should take place. Trisect follows the same rule. Also, -sect requires “equal parts”. But make no mistake, -sect does the cutting once, not bi-. Bi- means two parts not cutting twice.

    Here’s another example using the prefix bi-. Hetero-, homo-, and bisexual hold most definite meanings. Hetero- means other or different. Thus, a heterosexual is attracted to other than one’s own. Homo- means same. Then, a homosexual is attracted to one’s own. And bi- means both of the existing sexes, or the same AND something other than same, maybe even opposite. Bi- did not create two sexes, nor did it divide one sex into two. It only described the two sexes in existence. So bisexual loves both…two…not twice of the same. Much like bisect cuts into two, not twice, with -sect as the operative.

    Wouldn’t it be interesting to apply hetero-, homo-, and bi- to “weekly”. Heteroweekly would mean at some time other than this week. Homoweekly would mean during this or the same week. But look at this, biweekly would mean both this week AND the other…two. Remember, bisexuals don’t love the sexes twice, they love two sexes. And bisexual describes the sexes, not how many time they are loved.

    Couldn’t we deduce from this explanation that biweekly means there must be an occurrence of two weeks in order for something to happen, not that something happens twice in a single week?

    I understand the dictionary allows two meanings. But for me, biweekly is every two weeks and I will use “biweekly”. Thanks, y’all.

  45. Michael J says:

    It is one thing to acknowledge that a lot of people mis-use a word and therefore the well educated must be cautious when using that word around the less well educated. However, it is a wholly different thing to just cave in and say “the word by has taken on both meanings.” That is a cop out. The only way it was allowed to take on both meanings is because some set of “authorities” caved in and said it’s okay, it has now taken on both meanings. At exactly what point does mis-use become okay? Jane acknowledged that mute was incorrectly used where moot was meant. But by the standards being applied to “bi” it is just a matter of time before mute will have “taken on both meanings.” I call bull— and cop-out on this “process” for changing the meaning of words.

  46. Steve says:

    I think this contradiction between uses will lead to discontinued use of bi-weekly and bi-monthly unless an authority on word usage takes a stand.

  47. Greg says:

    …” If you mean every two weeks, you may also say, “I visit my aunt semimonthly.”
    For accuracy, I believe that bi-weekly would be more appropriate if this were the case. A year of semi-monthly visits would result in 24 visits while a year of bi-weekly visits would total 26.

    • says:

      As we stated in the blog, “You may want to substitute the actual time frame for these confusing terms.”

  48. rOx says:

    The true answer, I believe, is not in the placement of bi or semi prefix; both are equally ambiguous. Hence dissertations on the meaning of the prefix are meaningless. The answer, rather, lies in the meaning of the suffix “ly”.

  49. Paul Clark says:

    Even the “proper’ definition as quoted in thisarticle is can ‘bi-weekly’ mean BOTH “twice a week”,AND ‘every two weeks”? What good is THAT???

    • says:

      Perhaps you misread our blog. We did not identify any definition as “proper.” We reported what you will find if you look the words up in the dictionary. It is good that we inform our readers that these words can lead to confusion.

  50. Stanton says:

    Fortnightly anyone?

  51. Jake says:

    This was an interesting thread to read (and original article) to read. I thought I would just make a small contribution, in pointing out logical fallacies that seem to have consistently taken place (I will point no fingers though).

    * You must be careful when defining a word by latin roots (or greek for that matter) to a word, and come out with a ‘definitive’ definition. They give a basic background but seldom definitive meaning. IE: bi- as a prefix means “two”, that is all. It doesn’t mean every two, just two. A prefix is not predefined in two of what. (bi) weekly then can be seen as two-weekly (biweek[twoweeks]ly or two weekly (bi [two] weekly), based on the order of word construction.

    * You must be careful when defining a word by listing example that come to mind of how the prefix is interpretted in another word. Other examples provide evidence of possible usages, but not proof of specific use.

    * Acknowledging ‘multiple evolutions of language’ is rather necessary, for a language found all over the world. If “how it is supposed to be used” means “how it was first used”, then proper English will be primarily British..

    I mean, what is a biscuit? According to the Latin, twice-cooked. Definitely not the delicious golden goodness I enjoy under some good sausage gravy.

    • BobM says:

      You could really mess with their heads by using “semifortnightly” to indicate something that occurs every seven days.

      . . . . . “Every Monday at 10:00 AM we will have our semifortnighly staff meeting”

  52. Steve Garbee says:

    I see this differently. Consider weekly (or whatever) as the period of a repeating event. Bi- and Semi- are then modifers of the interval or period. I contend that using bi- infers the event occurs twice as often, i.e. twice per base period or twice per week. Semi- infers half, or that the event happens half as often, i.e. every two weeks.

    • MrStuff says:

      HEAR HEAR! If we’re going to ‘evolve’ language, this is how it should be. Imo, go with already established and unchanging definitions, if you BIsect an angle, you end up with two halves. So bi-anything should be every half of that anything, i.e. bi-yearly = twice a year.

  53. Terry says:

    In a headline or header when referring to an annual event should it be: 2nd or Second
    Does it follow the same rules as in number where all numbers under 11 are spelled out?

    • says:

      The Associated Press Stylebook is targeted to newspapers and magazines. In regard to headlines, AP’s rule says, “Use numerals for all numbers except in casual uses: “hundreds” instead of “100s.”

  54. Jery says:

    My boss asked me to submit a bi-weekly report on something. I came here to see if it meant 2 times a week or once in two weeks… seems I got more confused reading everything here…

    Also trying to read through, it came to me that the confusion erupts when ‘time’ is replaced with ‘an object’… English is a second language so I apologies if this makes people more confused. Let me explain what I mean…

    Biweekly = twice a week (time)?
    Bilingual = two languages (object)
    Biweekly report = object with time (confusion) what is the ‘bi’ pointing at, the report or the week?

    • says:

      Those are interesting thoughts, but the only way you can be sure is to ask your boss for clarification.

  55. nicky says:

    Why do people make immature comments

  56. Krylos says:

    I detect a fair bit of frustration in the posts being tossed about here and it certainly will not end with this thread. I, for one, certainly hope that it does not. For the frustrated, your angst is understandable as you seek closure, but I offer some perspective on the cost of closure. The issue surrounding the fate of “bi” and whether it has “devolved” to the current state is one of prescriptive and descriptive linguistics. Prescriptivists will argue that the use of “bi” has “devolved” in not coming closer to universal consensus and Descriptivists will revel in the fact that “bi” is still “evolving”–kudos to Jane/GrammarBook for throwing out both terms as it really does depend on which side of the fence you are on. I posit that the discussion here is dominated by “prescriptivists”, because, in regard to language, they hold clear communication above all else and hence, will seek out an authority to “solve the matter,” so to speak. Now, before you claim your camp in the war for linguistic superiority, note that the discussions here have been quite lively… linguistically speaking, that is of supreme importance. We, fortunately, IMHO, are dealing with a living language and this is but one evidence of how truly alive it is. There certainly are many valid arguments for prescriptivism, some of the foremost being in science where precision is paramount and in the business world where time is money and we don’t have the time or money to waste in figuring out what someone means when they say, “submit a bi-weekly report.” But, in your quest for clarity, don’t lose sight of how vital a living language is. Languages suffocate and die under conquerors, dictators, and other extreme duress. Yes, adults will complain of leet just as vehemently as teenagers will complain of Shakespeare, but rest assured that if your language is living and breathing, the people who use it are as well! Peace to you all.

  57. Dawn Parnell says:

    If you can have – bi-weekly and bi-monthly can you have bi-daily?

    • says:

      Theoretically, yes, but it’s not generally accepted, and it’s subject to the same misinterpretations as biweekly and bimonthly.

  58. Stuart says:

    This is obviously a late addition, but would it be easier if we broke the word differently? Weekly means once per week. Wouldn’t biweekly mean once per biweek or once per two-week? That would make semiweekly once per semiweek or once per half-week. We don’t use the terms biweek (fortnight) or semiweek, but looking at the construction, this has the merit of internal consistency. As for proscriptive or descriptive, I agree that the purpose of language is clear communication. To that end, we need some degree of standardization. The descriptive side of things will always be necessary since our world changes, our needs change and our language will have to change with them.

  59. MiddleEarthOrc says:

    This answer is bananas.
    Biweekly means once every two weeks or twice a week.
    Bimonthly means once every two months or twice a month.

    “once every two weeks or twice a week”? Are you saying it is either? Because those two things are very different.

    • says:

      Please see Jane’s reply of July 13, 2010, which applies perhaps even more so today than when she addressed the subject.

  60. Phil says:

    My confusion comes from order of operations:
    – (bi-week)-ly means happening every two weeks.
    – bi-(weekly) means two times weekly.
    Same applies to semi-:
    – (semi-week)-ly means every half week (or twice per week).
    – semi-(weekly) means half as much as weekly (or every other week).

    • says:

      The distinction between “bi-” and “semi-” only continues to blur in daily communication. Your observation reinforces our following statements in the article, particularly the second one:

      Those of us who resolutely uphold precision might cling to Latin’s original intent for bi and semi: bi = two, semi = half (or twice). Such loyalty to Latin would give us biweekly for “every two weeks” and semiweekly for “twice a week.”

      Conversely, those of us who note that the blurring of bi and semi will only get greater will avoid confusion altogether by stating the actual time frame. Instead of battle with biweekly or semiweekly, we will say “every two weeks.” Rather than wrestle with bimonthly or semimonthly, we will write “twice a month.”

  61. Simon says:

    What is the term for half-quarterly? Currently I do a report quarterly , but I want to change the report so it’s completed eight times a year, not four.

    • says:

      To refer to a report that is issued twice each quarter, you can refer to it as a “biquarterly report.”

  62. James J. Kaufmann says:

    Welcome to the world of linguistics, where language is described, rather than prescribed. I found it helpful to confirm my suspicion about the confusion that can arise from the actual usage of these words. Knowing this helps us to find a way to greater clarity for a given audience or context.

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