"Thirty Days Hath September", or "Thirty Days Has September",[1] is a traditional verse mnemonic used to remember the number of days in the months of the Julian and Gregorian calendars. It arose as an oral tradition and exists in many variants. It is currently earliest attested in English, but was and remains common throughout Europe as well. Full:
Thirty days has September,
April, June, and November,
All the rest have thirty-one,
Save February at twenty-eight,
But leap year, coming once in four,
February then has one day more.
An alternative version goes:
Thirty days hath September,
April, June, and November,
All the rest have thirty-one,
Except February, twenty-eight days clear,
And twenty-nine in each leap year.