Date Calculator

Counting days between two dates

The calculator counts the days you would step through on a calendar going from the start date to the end date: 1 January 2026 to 1 November 2026 is 304 days. The count excludes the start date and includes the end date, which is the convention most countdowns, deadlines and booking systems use — if you count both endpoints, add one, and that off-by-one is the single most common date-arithmetic mistake.

Weeks are just the day count divided by seven (304 days is about 43.4 weeks), but months resist neat conversion: months are 28 to 31 days long, so “three months from now” depends on which months. The calculator therefore gives an approximate years-and-days breakdown rather than a false-precision month count, and our age calculator handles full years-months-days breakdowns for birthdays.

Adding and subtracting days

Adding days is how deadlines, notice periods and delivery estimates are actually worked out: a 30-day notice served on 1 November 2026 ends on 1 December 2026, and a 90-day project starting 5 January 2026 lands on 5 April 2026. The calculator steps across month and year boundaries, including 29 February in leap years, so you never have to work out by hand whether the span crosses one.

Business-day counting is a different job: it skips Saturdays, Sundays and public holidays, and the number of working days in “30 days” depends on the calendar and the country. This calculator counts calendar days throughout; if a contract says “30 working days”, count only Monday-to-Friday days and check the local holiday list for the period.

Leap years and calendar quirks

A year is a leap year if it divides by four, except centuries, which must divide by 400 — so 2024 was a leap year, 2100 will not be, and 2000 was. The extra day sits at the end of February, which is why spans crossing February differ by a day depending on the year: 1 February to 1 March is 28 days in most years and 29 in a leap year.

The calculator uses the Gregorian calendar throughout, the system in civil use almost everywhere today, and works in UTC dates so that time zones cannot shift a result by a day. Historical dates before the Gregorian reform, or calendars other than the Gregorian, need specialist tools — this one is for the dates people plan around now.