Days in Month Calculator

How to use

1. 1Keep Days in one month selected, choose a month from the list, and type a year between 1 and 9999 (today's month and year are filled in for you).
2. 2Read the result: the number of days, the weekday the month starts and ends on, the ISO date range, and a one-line explanation of why the month has that length.
3. 3For February, note the leap-year reason; the day count switches between 28 and 29 automatically based on the year you enter.
4. 4Switch to Every month in a year to see all twelve months for a year at once, with each month's length, its starting weekday, and the 365 or 366 day total.
5. 5Use Copy summary or Copy table to grab the result as text, or use This month to jump back to the current month. Everything runs in your browser.

About this tool

Days in Month Calculator answers a question people look up constantly: how many days are in a given month? Pick any month and any year from 1 to 9999 and the tool returns the exact day count (28, 29, 30, or 31), the weekday the month begins on, the weekday it ends on, and the full date range in ISO form, so you can answer how many days are in February 2026 or what day September 1 falls on without flipping through a calendar. Seven months always have 31 days (January, March, May, July, August, October, and December), four months always have 30 days (April, June, September, and November), and February is the only month whose length changes: it has 28 days in a common year and 29 in a leap year. The tool applies the Gregorian leap-year rule for you, so February only shows 29 days in years that actually have it, and it explains which branch of the rule decided the answer (divisible by 4, the divisible-by-100 century exception, or the divisible-by-400 override that makes 2000 a leap year while 1900 and 2100 are not). Switch to the year view to see all twelve months at once for any year, with each month's day count, the weekday it starts on, the current month highlighted, and the total of 365 or 366 days in that year. Because only February ever varies, a year is always either 365 or 366 days long, and the full-year table makes the pattern easy to read for planning schedules, building date pickers, checking payroll periods, or fact-checking a date. The page also includes two classic ways to remember month lengths without any tool: the thirty days hath September rhyme and the knuckle trick, where each raised knuckle is a 31-day month and each dip between knuckles is a shorter one. Every result is computed locally with plain calendar arithmetic, so the months and years you check stay on your device with no signup, no upload, and no tracking. It pairs naturally with the leap year calculator for the full divisibility rule, the date difference calculator for counting days between two dates, and the working days calculator for business-day totals.

Free to use. Works in your browser. No signup, no login.