I would like to know if there are any terms to represent a month with 30 days or 31 days respectively.

Big month? Leap month?

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    A leap month is an extra intercalary month inserted between two regular months. Leap months do not occur in the Gregorian calendar, which is the calendar used in most English-speaking countries.
    – user230
    Commented Mar 22, 2013 at 17:49
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    Do you mean, are there separate terms for 30-day months vs 31-day months? Or do you mean a term for non-February months? If the former see knuckles entry Commented Mar 22, 2013 at 18:38
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    I found this, concerning the Jewish calendar: “A month of 30 days is called male ('full'), one of 29 days is chaser ('defective').” Also related, this ELU question. I think it's safe to say that, if English does have words for 30- and 31-day months, those words are rarely used and seldom heard.
    – J.R.
    Commented Mar 23, 2013 at 0:55
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    @Ivan: Even or odd would not be a good way to say it. As snailplane points out, most people would consider the "even" months to be Feb, Apr, Jun, Aug, Oct, and Dec – two of those months have 30 days, and three of them have 31, thanks to the consecutive 31-day months of July and August. You could use full and short, but I'd probably be inclined to go with "31-day_month" to keep ambiguity at a minimum.
    – J.R.
    Commented Mar 24, 2013 at 9:26
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    @J.R. That's true. Everyone understand "30-day months" so I will use that instead. Thanks.
    – Ivan Chau
    Commented Mar 24, 2013 at 9:49

2 Answers 2


If you want separate terms to refer to 30-day months and 31-day months, I doubt you'll do better than 30-day months and 31-day months.

Even and odd sound nice, but they have an unfortunate flaw: people use them to refer to even- and odd-numbered months! That is, months 1, 3, 5, 7, 9 and 11 are odd; months 2, 4, 6, 8, 10, and 12 are even.

The term knuckle month sounds nice, too, but not everyone will get the reference, I'm afraid. I'm certain of this because I just talked to a friend a couple weeks ago who was unfamiliar with the knuckle mnemonic.

You can, of course, use a term like knuckle month or odd month, as long as you're careful to tell people what you mean by it. But if your goal is to communicate without further explanation, I would avoid looking for special terms like these (fun as it may be) and simply state the number of days.

  • In Hong Kong, I believe most of the people know the idea of knuckles mnemonic. Though people may not recognise meaning of the term "knuckle month" immediately.
    – Ivan Chau
    Commented Mar 24, 2013 at 5:16
  • Thirty days hath September April, June, and November All the rest have thirty-one But February's twenty-eight The LEAP YEAR, which comes once in four Gives February one day more Useful? Probably not, but when else will I get to use that rhyme? edit this would look better if I could get line breaks to work Commented Sep 2, 2020 at 21:34

I'm late to the party but it might be useful to know. At my former employer, we called them standard and extended (as in standard-length month and extended-by-one-day month). February was referred to as leap or extended leap, depending on the year.

The March and October were sometimes referred to as increased and decreased because of the one-hour offset when the daylight saving kicks in and out.

So there was expressions like accumulated work hours in the extended and non-decreased months. Not surprisingly, the nomenclature was as painful as it was precise.

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