Days Between Dates Calculator

How the days are counted

The number of days between two dates is the later date minus the earlier one. From Monday to Friday is 4 days; from today to tomorrow is 1. This is the count you want for “how many days until” and “how many days since” questions, and it’s what the calculator shows by default.

Tick Include the end date when both the first and the last day should count — the days of a holiday, an event or a hotel stay counted as dates rather than nights. That adds exactly one day. Monday to Friday counted this way is 5 days.

The same gap is also shown in weeks, in calendar months and in years, months and days. The weekday count covers exactly the days that were counted: the start date up to, but not including, the end date — or up to and including it when the end date is included. Weekdays plus weekend days always equal the total.

Formula

Each date is turned into a serial day number — a count of days from a fixed point — and the two are subtracted:

Weekdays come from whole weeks first, because any 7 days in a row contain exactly 5 weekdays:

N(date)

serial day number of the date (Howard Hinnant’s days-from-civil algorithm)

⌊x⌋

x rounded down to a whole number

Serial day numbers make leap years automatic: on the Gregorian calendar a year divisible by 4 is a leap year, except century years that aren’t divisible by 400. The months-and-days figure counts whole calendar months from the earlier date, then the days left over.

Worked example

From Thursday, 1 January 2026 to Friday, 25 December 2026:

1. 25 December is day 359 of 2026 and 1 January is day 1, so the difference is 359 − 1 = 358 days.
2. 358 ÷ 7 = 51 weeks with 1 day left over.
3. 1 January + 11 months = 1 December, then 24 more days: 11 months, 24 days.
4. Weekdays: 51 full weeks × 5 = 255, and the one leftover day, 24 December, is a Thursday, so 256 weekdays and 358 − 256 = 102 weekend days.

Including the end date, the answer is 359 days: 51 weeks and 2 days, 11 months and 25 days, and 257 weekdays, because 25 December 2026 is a Friday.

Good to know

• End date before the start date. The result is shown as a negative number of days instead of an error, and the weeks, months and weekday counts are those of the same days in date order. Use Swap to flip the dates.
• Business days. The weekday count takes out Saturdays and Sundays only. Public holidays depend on the country, region and employer, so subtract any that fall in the period yourself.
• Nights versus days. A stay from the 1st to the 5th is 4 nights; counted as dates it is 5 days. Use the default for nights and the end-date option for dates.
• Dates, not times. Each date counts as a whole day, whatever the time or time zone. For hours and minutes, use the time calculator.