Which month has only 28 days and every 4 years has 29?

A year has 365 days divided into 12 months in the modern day Gregorian calendar. Each month has either 28, 30 or 31 days during the common year. Nearly every 4 years is a Leap Year with 366 days because we add an extra (intercalary) day at the end of February, the Leap Day on 29 February. February is the only month that is 28 days long in common years and 29 days long in leap years.