April is month number

How it works

Months in the civil calendar used by most of the world are numbered from January. January is 1, February is 2, March is 3, April is 4, then May 5 through December 12. Searches for april number month and april month number want that ordinal. They do not want a feast called “April.” Write April as 4, or as 04 when a form wants two digits. ISO 8601 dates write the month in the middle of year-month-day, so 2026-04-15 is 15 April 2026. The 04 is the same four.

April always has 30 days in the Gregorian calendar. It does not gain a 31st. It does not shrink in a leap year. Leap day belongs to February. Weekdays of 1 April change every year. The month number does not. Software that stores months as numbers from 0, as some programming libraries do, will call April 3 if January is 0. That is an index, not the civil number. If a form rejects “April” and wants a digit, give 4 unless the documentation says the field is zero-based.

The English name April comes from Latin Aprilis. Older Roman numbering once counted March as the first month, which is why September through December still look like seven through ten. April’s civil number today is still four, because January and February sit in front of it in the year we actually use. Do not “correct” April to month 2 because of that ancient March-start. You will break every airline ticket.

Why April is four, and what that is not

Four is a position, not a festival. No country takes the month number off as a holiday. People mix the question with April observances that do have dates: 1 April as April Fools’ Day, a custom of jokes, not a public closing in ordinary national law; Earth Day on 22 April as an environmental mark from 1970; ANZAC Day on 25 April as a public holiday in Australia and New Zealand. Easter often falls in April because it is a movable Sunday after the paschal full moon, but Easter is not “month number 4.” When Easter is in March, April is still four.

Fiscal years complicate labels without changing the month. A U.S. federal fiscal year begins in October, so April is month 7 of that fiscal year and still month 4 of the calendar year. A school year that starts in August treats April as late spring term. Say which year you are counting. The civil month number stays 4.

Calendar month number: April = 4 (or 04). Length: 30 days, leap year or not. ISO 8601: YYYY-04-DD. Zero-based computer indexes: may store April as 3; read the docs. Not a holiday: the number 4 does not close an office.

April is four because January took one. The month does not need a parade to keep its place in line.

Writing the number so the next person can read it

If you need a machine field, prefer 04 to “Apr” when the other side is not English. If you need a human heading, “April” beats “month 4” except on this page, where the question was the number. Do not write 4/5 when you mean 5 April unless you have already agreed the American month-day order. 4/5 is 4 May in day-month countries and 5 April in month-day countries. ISO dates remove that fight: 2026-04-05 is 5 April.

Quarter numbering follows months: April begins the second quarter of a calendar year (Q2 is April, May, June). That is useful for accounts. It is still not a holiday. Tax days, school holidays, and spring breaks that happen to land in April are other rules. They borrow the month. They do not redefine it.

If the query was “what number month is April,” stop at 4. If the query was “what holidays are in April,” name the country, then the dates. This page is the number. Keep the number boring. Boring is what makes calendars work.