Date Difference Calculator

Count days between dates for plans, SLAs, and leave

Date-difference math powers project buffers, pro‑rata refunds, rental day counts, and HR leave accruals. Leap years and month lengths are baked into civil-date libraries; this page mirrors those rules in the browser.

Contrast calendar days vs business days if your contract mentions “5 business days”—that requires a separate holiday calendar this tool does not model.

Pair with the timezone converter when midnight boundaries span zones, and the cron generator when schedules are periodic rather than one-off spans.

For legal deadlines, always verify jurisdiction-specific rules; calculators are aids, not counsel.

How the difference is counted

The headline figure is the number of calendar days from the start date to the end date: the start date is not counted and the end date is — the same result as subtracting one date from the other, or counting nights in a hotel. Monday to Friday is 4 days. If you need to count both the first and last day, add 1.

Below it, the same span is broken down into whole years, months and days, counted the way a calendar works rather than by dividing by 30: 1 January to 25 December 2026 is 11 months and 24 days, or 358 days. When the start day does not exist in a shorter month, the month counts as complete on its last day, so 31 January to 28 February is exactly one month.

Dates are read in your own time zone, and daylight-saving changes never add or remove a day. If the end date is before the start date, the tool shows how long ago it was instead.

Worked examples

• Leap years: 1 February to 1 March 2024 is 29 days; the same dates in 2026 are 28 days apart.
• Deadlines: 90 days after 2 October 2026 is 31 December 2026. Check whether your contract counts the day of notice itself — some legal deadlines do.
• Weeks: 358 days is 51 weeks and 1 day, shown as the weeks figure plus remaining days.
• Project buffers: if a release is due on 15 March and today is 1 February, there are 42 days left, or 6 weeks.

Calendar days, business days and deadlines

This tool counts calendar days. Many contracts, shipping estimates and government processes use business (working) days instead, which skip weekends and public holidays — use the business days calculator for those. Also check how a deadline is phrased: “within 30 days of” usually starts counting the day after the event, while “by day 30” can include it. When money or legal rights depend on the answer, confirm the rule with the other party or an adviser.

Calendar facts behind the numbers

• Leap years: a year is a leap year if it is divisible by 4, except century years, which must be divisible by 400 — 2000 was a leap year, 2100 will not be.
• A common year has 365 days (52 weeks and 1 day); a leap year has 366.
• Month lengths repeat on a pattern: 31 days in January, March, May, July, August, October and December; 30 in April, June, September and November; February has 28 or 29.
• For hours, multiply days by 24 — 358 days is 8,592 hours — but local clocks gain or lose an hour on daylight-saving days.