How Many Months Have 28 Days?

The trap in the question

Most listeners hear "which month has 28 days?" and answer February. The riddle asks for a count, and the count is twelve. Every month has at least 28 days: January has 31, April has 30, and so on, so each of the twelve contains a stretch of 28 days. February is simply the only one that stops there.

The wording does the work. "Have 28 days" sounds like "have exactly 28 days", and the mind answers with one month. Once the question is heard as "at least", the answer is plain.

Where leap years come in

February has 28 days in an ordinary year and 29 in a leap year. Under the Gregorian calendar a year is a leap year when it divides by 4, except that a century year must also divide by 400. That is why 2000 was a leap year, 1900 was not and 2100 will not be. The next February 29 falls in 2028.

A follow-up for the group

Once the answer lands, a second question keeps the game going: how many months have 31 days? The answer is seven: January, March, May, July, August, October and December. Asking it right away lets the listeners count the months for themselves.