Does bimonthly mean twice a month or every two months?

The prefix bi- usually means ‘every two’, so bimonthly means ‘every two months’.Semi- means ‘half’ or ‘halfway’, so semimonthly means ‘every two weeks’. However, bimonthly can also mean ‘twice a month’ – but it is rarely used that way. It is best to remember that bi- is “every two” and semi- is “halfway.”


  1. Humayun Mirza -  October 29, 2016 - 12:43 am

    So finally, how should one call, say, a magazine published once every two months? Is there an unambiguous alternative to bimonthly?

  2. Shawn -  September 15, 2016 - 4:50 am

    ‘Bi-’ prefix is ambiguous where bimonthly kan mean either twice a month or every 2 months, altho its true/accurate meaning is ‘two’ thus bimonthly is only accurately once every two months.
    ‘Semi-’ prefix is *not* ambiguous. Semimonthly only means every half month.
    The ambiguity of ‘bi-’ is only because people incorrectly and frequently use ‘bi-’ when meaning ‘half’ instead of ‘every two’.

  3. Andrea -  September 6, 2016 - 11:02 pm

    biannual = twice a year
    biennial = every other year

    Easy hint: The Venice Biennale takes place every other year.

  4. Donald Rajaseelan -  July 21, 2016 - 7:08 am

    bi – stands for twice, so bi-monthly means twice a month, bi-weeekly means twice a week, bi-annual means twice a year.

    • Lewis -  August 30, 2016 - 1:28 am

      This comment is flat-out wrong. If bi-monthly means twice a month, bi-weekly means twice a week, and bi-annual means twice a year, then the United States would have celebrated its bi-centenial every 50 years — four times already, with a fifth bi-centenial just ten years from now. That’s clearly not the way it works: bi means “every two” so bi-monthy is once every two months, bi-weekly once every two weeks, bi-annual once every two years, and bi-centential once every two centuries.

      • Karyn Heath -  November 27, 2016 - 6:24 pm

        Bi-annual does mean twice a year. Biennial means once every two years

  5. . -  May 19, 2016 - 9:09 am

    doesn’t “bi-annual” mean twice a year? that seems to be opposite of the more common definition of “bi-monthly” meaning every other month (??)

    • Adam -  June 18, 2016 - 2:19 am

      Unlike the “bimonthly” ambiguity, “biannual” has two distinct words to clarify the writer’s intent, leading me to avoid using “biannual” altogether:
      - “semiannual” means twice a year.
      - “biennial” means every two years.
      Confusion averted!

  6. Mitch -  May 18, 2016 - 12:33 pm

    And Karen has nicely demonstrated the confusion. She’s trying to draw a distinction between biweekly and semi-monthly. Not being a payroll guy, I wonder if the accounting world has solidified the confusion by using the word ‘bimonthly’ (instead of ‘semi-monthly’) to mean ‘twice a month.’

    • Allen -  August 22, 2016 - 10:44 am


      In the payroll world, bi-weekly results in 26 pay period per year while semi-monthly results in 24 pay periods in a year. There are two months each year that has three payrolls in the given month on a bi-weekly basis.

  7. Tom Jennett -  April 8, 2016 - 11:11 am

    The article above is correct. But because the confusion around the word is so pervasive it’s probably best just to say “every other month” instead of bimonthly. The word often occurs in contexts where schedules and deadlines are important. I’ve seen the word used incorrectly in istructions for a government form where filing it late meant a penalty – and good luck telling some bureaucrats their usage is wrong. Clarity is king. “Semi-monthly” is okay and doesn’t seem to present the problem.

    • Russell -  April 16, 2016 - 5:31 pm

      for those in countries influenced by England, perhaps fortnightly is better if it’s to mean twice a month. Do those in the US use the word “fortnight” (short for fourteen nights – 2 weeks)?

      • Karen -  April 29, 2016 - 6:18 am

        Bimonthly and fortnight do not mean the same thing. Biweekly (every two weeks) would be similar to fortnight. Eg a biweekly payroll would mean paid on the same day of the week every second week (26 times per year). A bimonthly payroll typically means paid on the 15th and last day of month (24 times per year).

      • Shawn -  September 15, 2016 - 4:40 am

        dude, twice a monthly and every two weeks are *not* the same. they are similar and close, but still have an important difference. no, in the US, we do not use ‘fortnight’ and few know the word. but some of us do know the word. fortnightly wud *not* mean twice a month. fortnightly wud mean every two weeks.

        • Gene -  October 11, 2016 - 9:49 am



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