Days in Month Calculator

Seven months have 31 days (January, March, May, July, August, October, and December), four months have 30 days (April, June, September, and November), and February has 28 days in a common year or 29 days in a leap year. A quick way to remember the long months is to use your knuckles: each knuckle is a 31-day month and each dip between them is a shorter month.

It applies the Gregorian leap-year rule. A year is a leap year if it is divisible by 4, except that years divisible by 100 are not leap years unless they are also divisible by 400. So 2000 and 2400 are leap years and February has 29 days, while 1900 and 2100 are common years with 28 days in February.

February is the only month with a variable length because the leap day is added to it. A solar year is about 365.2422 days, so an extra day is inserted roughly every four years to keep the calendar aligned with the seasons. That extra day becomes February 29, making the month 29 days long in leap years and 28 days the rest of the time.

The calculator shows the weekday of both the first and last day of the month, computed with Zeller's congruence for the Gregorian calendar. For example, February 2024 starts on a Thursday and ends on a Thursday. This is handy for planning schedules, payroll periods, or rota patterns.

You can enter any Gregorian calendar year from 1 through 9999. The results use the proleptic Gregorian calendar, meaning the modern leap-year rules are projected back before the calendar was actually adopted in 1582, which keeps day counts consistent across the whole range.

The calculator counts each day from the first to the last, marking Saturday and Sunday as weekend days and the rest as weekdays. A 28-day February has exactly 20 weekdays and 8 weekend days, while longer months shift depending on which weekday the month starts on. This breakdown is useful for estimating working days in a month.