What Is A Calendar Month. One of the twelve named months that the year is divided into: The period of duration from the same date of one month to the same date of the next month, and thus can be 28, 29 during a leap year, 30 or 31 days long.

A calendar month is the period from a particular date in one month to the same date in the next month, for example from april 4th to may 4th. A “month” and a “calendar month” usually mean the same thing, but not always.