Date Calculator: Days Between Dates and Add or Subtract Time

  • Free
  • No sign-up
  • Runs in your browser
  • Version 1.0.0
  • Last updated 2026-10-07
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Find how long it is between two dates, or what date it is after adding or subtracting some time.

Days between two dates

Add or subtract time

Everything you enter is processed in your browser and is never sent to a server.

How to use

  1. For a gap, pick the start and end dates. The days, weeks, years-months-days and weekdays appear at once.
  2. For a new date, pick the starting date and enter years, months and days. Use a minus sign to go back.
  3. Read the result with its weekday, the day of the year and the ISO week number.

Examples

2026-01-01 to 2026-12-25
→ 358 days, 51 weeks 1 day, 0 years 11 months 24 days
The start day is not counted; the difference is the end date minus the start date.
2026-01-31 plus 1 month
→ 2026-02-28
February has no 31st, so the result is the last day of the month.
2026-10-07 plus 100 days
→ 2027-01-15

How it works

Dates are read as year-month-day and turned into days since 1970 at UTC midnight, so the difference between two dates is an exact whole number of days. The years, months and days breakdown moves the earlier date forward by whole months first, then counts the remaining days. Weekdays count Monday to Friday in the span from the start up to, but not including, the end date; public holidays are not considered.

The tool is tested with the examples on this page, leap years, month-end clamping and the ISO week edge cases of 2021, 2024 and 2026.

Sources

Frequently asked questions

Is the start date counted?
No. The count is the end date minus the start date, so 2026-10-07 to 2026-10-08 is 1 day. Add 1 if you want to count both ends.
How are months added when the day does not exist?
The result is the last day of the target month. January 31 plus one month is February 28, or 29 in a leap year. Months are added before days.
Do time zones or daylight saving change the answer?
No. Dates are treated as calendar days with no time of day, so a clock change never adds or removes a day.
What is an ISO week?
ISO 8601 weeks start on Monday, and week 1 is the week with the year's first Thursday. Early January can fall in week 52 or 53 of the previous year, and late December in week 1 of the next.
Are my dates sent anywhere?
No. All calculations run in your browser.
Version history
  • 1.0.0 — First release.

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