How to count the days between two dates

How many days until a wedding, since a project started, or between invoice and payment? Counting on a calendar works for short spans and goes wrong for long ones, because months have different lengths and some years have 366 days.

Count days with the age calculator

An age calculation is a count between two dates, so the Age Calculator works for any pair of dates:

1. Enter the earlier date as the date of birth.
2. Enter the later date as “Age at this date”.
3. Read the total days, along with total weeks, months and the difference in years, months and days.

Example: from 14 March 2026 to 25 December 2026 is 286 days. From 3 October 2026 to 1 January 2027 is 90 days.

Include the end date or not?

A date calculator counts the gap between dates, which excludes one end. From Monday to Wednesday is 2 days. If you are counting days of an event that includes both the first and last day, such as a hotel stay or a leave period, add one: a conference from Monday to Wednesday lasts 3 days.

• Nights in a hotel: the gap (check-in to check-out). Monday to Wednesday is 2 nights.
• Days of leave or of an event: the gap plus one. Monday to Wednesday is 3 days.
• Days until a deadline: the gap. Counting down from today, today is not included.

Counting by hand

Remember the month lengths:

• 31 days: January, March, May, July, August, October, December.
• 30 days: April, June, September, November.
• February: 28, or 29 in a leap year (2028 is the next).

Count the days left in the first month, add every full month in between, then add the days in the last month. For 14 March to 25 December: 17 (rest of March) + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 (April to November) + 25 = 286.

Weeks and months

Divide days by 7 for weeks: 286 days is 40 weeks and 6 days. Months are trickier because they are not all the same length. “Three months from 31 January” is ambiguous. For contracts and notice periods, use the wording of the agreement, which usually counts calendar months to the same date. To convert days into hours, minutes or average months and years, use the Time Converter.

Working days

Business deadlines often count working days only, excluding weekends and public holidays. A quick estimate: total days × 5 ÷ 7, then subtract the public holidays in the period. For anything with legal consequences, count on a calendar that shows your local holidays.

Time zones

For dates in different time zones, such as a flight that crosses the date line, count in one zone. For meetings across zones, see scheduling a meeting across time zones.