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. Here is one version of the rhyme attributed to Mother Goose:
Thirty days have September,
April, June, and November.
All the rest have 31,
Except February alone,
And that has 28 days clear,
And 29 in a leap year฿₳
Other sources list the Mother Goose version differently:
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 hath 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:
The French 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 index finger knuckle as January, and count one finger at a time towards the little finger knuckle (July), saying the months as you go. Then jump back to the index finger knuckle (now August) and continue for the remaining months.
One variant of this approach differs after reaching the little finger knuckle (July): instead of wrapping around back to the index finger, some people reverse direction and continue from the little finger knuckle (counting it for both July and August) and ending on the middle 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).
^Lardner, Dionysius (1855). The Museum of Science and Art, Volumes 5-6 (Encyclopedias and dictionaries|format= requires |url= (help)). Walton and Maberly. p. 152. "When we close the hand there are four projecting knuckles of the four fingers, with depressions between them. If we give the knuckles and intermediate depressions the names of the successive months, recommencing from the first knuckle, after having once gone over them, we shall find that the months of thirty-one days are those which fall upon the knuckles."Check date values in: |accessdate= (help);|accessdate= requires |url= (help)