Thirty days hath September

Thirty days hath September is a traditional English mnemonic rhyme, of which many variants are commonly used in English-speaking countries to remember the lengths of the months in the Julian and Gregorian calendars. See also Knuckle Mnemonic.

Here is one version of the rhyme attributed to Mother Goose:

Thirty days hath September,

April, June, and November.

Thirty-one hath all the rest,

Except for February clear which has 28 and 29 in a leap year.

Thirty days hath September,

April, June, and November

All the rest have 31,

Except for February.

Thirty days hath September,

April, June and November

All the rest have thirty-one

But February's but how much

History

The web site On This Day in Math dates the rhyme at least to 1488. "The Plimpton Library has a copy of Anianus, Computus Manualis combined with Boethius, Arithmetica, which is probably the first book on mathematics printed in Strasburg. It has the first known printing of the little mnemonic that begins, “Thirty days hath September,” in Latin.

Later versions differ from the medieval version in that September and November are often reversed, as in the Mother Goose variants above. As with any text that is still primarily transmitted orally, many versions exist. The first two lines are usually similar, with variations in the final lines relating to February. For instance, here is an unusual version that is longer and more rhythmic, with paired rhyming lines:

Thirty days have September,

April, June, and November.

All the rest have thirty-one,

no exceptions, but save one:

twenty-eight hath February,

but from this we still must vary

each four years when we do find

a small leap to twenty-nine.

A shorter version that rhymes perfectly is from an unknown source and date:

Thirty days have September,

April, June, and November;

Thirty-one the others date,

Except in February, twenty-eight;

But in leap year we assign

February, twenty-nine.

An old version that was traditionally sung (source unknown) is:

Thirty days hath September,

April, June, and November.

All the rest have thirty-one,

Except February alone,

Which has twenty-eight, in fine,

And each leap year twenty-nine.

Modern variants

Thirty days hath September, April, June and November; All the rest have thirty one --no wait! February's days count 28! Except in leap year, that's the time When February's days count 29

It is common to encounter derivative or shorter variants of the two Mother Goose versions above that have an imperfect or irregular rhyme pattern and rhythm:

Thirty days hath September,

April, June, and November;

all the rest have thirty one

Except February, on its own

which has twenty eight most times

And in a leap year, twenty nine.

Thirty days hath September,

April, June, and November;

all the rest have thirty one

February, only, twenty-eight;

leap years we assign

February, gets twenty-nine.

Thirty days has September,

April, June, and November.

All the rest have thirty-one,

Except—you know which one.

Thirty days has September

April, June, and November.

All the rest have thirty-one,

Excepting February alone

To which we twenty-eight assign,

'Til leap year gives us twenty-nine.

Thirty days has September,

April, June and November.

All the rest have thirty-one,

Excepting February alone

Which has eight and one score

And every fourth year one more.

Thirty days has September

April, June, and November.

All the rest have Thirty-One—

Well, all the rest but one.

February only has twenty-eight,

And that's just fine,

Except for every fourth year,

When February has twenty-nine.

Thirty days has September,

April, June and November;

All the rest have thirty-one,

Except for February which has twenty-eight,

Except in a leap year when it has twenty-nine!

Thirty days has September,

April, June, and November;

Once short February's done,

All the rest have thirty-one.

Thirty days has September

April, June, and November.

Of twenty-eight there is but one,

And all the rest have thirty-one.

Thirty days has September,

April, June, and November;

All the rest have thirty-one,

Except February. It has twenty-eight, we find,

Unless it's leap year: Then it has twenty-nine.

Thirty days has September,

April, June and November,

All the rest have thirty-one

Except for February alone, my dear

Which has twenty-eight, and twenty-nine in each leap year.

Thirty days has September,

April, June and November.

All the rest have thirty-one,

Except for February: It is done

At twenty-eight, but leap one more

When the year divides by four.

Thirty days have September,

April, June, and November.

All the rest have thirty-one,

save February which, alone,

has twenty-eight and one day more

we add to it one year in four.

Thirty days hath September,

April, June and November.

All the rest have 31,

excepting February alone,

which only has but 28 days clear

and 29 in each leap year.

One modern version forgoes describing February's exception to keep the rhythm and rhyme constant:

Thirty days have September,

April, June, and November.

All the rest have thirty-one,

Except for February—and that's no fun!

Another modern version also provides a reminder of St. Valentine's Day:

Thirty days hath September,

April, June, and November

All the rest have thirty-one,

Except the month of Valentine

Which, in leap year, has twenty-nine.

More elaborate variations, such as these, can be sung to melodies:

Thirty days has September,

April, June, and November,

All the rest have thirty-one,

except for February alone,

which has twenty-eight rain or shine,

but on leap year, twenty-nine.

Thirty days has September,

April, June, and November,

All the rest have thirty-one,

except for February alone oh no,

which has three less than the others rain or shine,

but on leap years, twenty-nine.

Thirty days has September,

April, June, and November;

All the rest have thirty-one,

except for February alone,

which has four and twenty-four,

'til leap year gives it one day more.

Thirty days has September,

April, June, and November;

All the rest have thirty-one,

except for quite contrary, February,

which has twenty-eight most of the time,

but in leap year twenty-nine.

Thirty days has September,

April, June and November.

All the rest have thirty-one,

save for February alone.

And then in leap year that's the time

that February has twenty-nine.

Thirty days has September,

April, June and November.

All the rest have thirty-one,

February has twenty-eight alone.

Leap year coming one in four,

February has one day more.

A humorous couplet sacrifices mnemonic utility for rhyme and brevity:

Thirty days hath September,

All the rest I can't remember.

This is one Swedish version:

Trettio dagar har september,

April, juni och november.

Februari tju'åtta allen,

Alla de övriga trettioen.

Translated to English:

Thirty days have September,

April, June and November.

February twentyeight alone,

All the others, thirty-one.

Knuckle Mnemonic

The knuckle mnemonic.

The German, French, Swiss, Romanians, Slovenes, Russians, Greeks, Danish and Belgians typically use a mnemonic by counting on the knuckles of one's hand to remember the numbers of days of the months. Count knuckles as 31 days, depressions between knuckles as 30 (or 28/29) days. Start with the little finger knuckle as January, and count one finger or depression at a time towards the index finger knuckle (July), saying the months as you go. Then jump back to the little finger knuckle (now August) and continue for the remaining months.

One variant of this approach differs after reaching the index finger knuckle (July): instead of wrapping around back to the little finger, some people reverse direction and continue from the index finger knuckle (counting it for both July and August) and ending on the ring finger knuckle.

Still others use two hands (as shown in the diagram, right): starting with the little finger knuckle of the left hand, proceed to the left index finger knuckle, then (swapping hands) jump to the right fist's index finger knuckle for August, finishing on the knuckle of the right ring finger (December).