Date Calculator

How to use it

Pick what to work out with the chips at the top. The result updates as you change a field.

1. Days between counts from the Start date to the End date. The big number is the calendar days between them. Under it are the whole Weeks and Months, and a table that splits the gap into weeks and days, months and days, and years, months and days, with each date’s weekday.
2. Tick Count business days, Monday to Friday to add a Business days count. It includes both dates; the row Weekdays, end date left out gives the count without the end date.
3. Add or subtract moves the Start date, then add to it by the Years, Months, Weeks and Days you type; a minus in front moves it back. The chips 30 days, 2 weeks, 90 days, 6 months and 1 year fill the fields in one click. The result is the new date as YYYY-MM-DD with its weekday, a Copy button and Days moved.

Each date field has a Today button that fills in your local date. Dates are whole calendar days with no time or timezone, so a daylight saving change can’t shift a count by one.

Examples

Days between with business days ticked, from 2026-10-14 to 2026-12-25:

72 calendar days
10 Weeks    2 Months    53 Business days

Weeks and days                10 weeks 2 days
Months and days               2 months 11 days
Years, months and days        2 months 11 days
Weekdays, end date left out   52
Start                         Wednesday, 14 October 2026
End                           Friday, 25 December 2026

The 53 counts 25 December itself, a Friday. Public holidays aren’t removed.

Add or subtract with the 90 days chip, from 2026-10-14, gives 2027-01-12, a Tuesday, with Days moved 90.

Months 1 from a month end, 2025-01-31, gives 2025-02-28 and this line under the result:

31 January 2025 plus 1 month is 31 February 2025. February 2025 has 28 days, so the date clamps to the last of them, 28 February 2025.

With Months 2 the same start gives 2025-03-31, because the months are added in one step. One month on from 2025-02-28 is 2025-03-28, so two single steps land three days earlier.

Good to know

• The day count is the end minus the start. From 2026-10-14 to 2026-10-15 is 1 day. To count both the first and the last day, as for the length of a trip, add 1. Business days count both ends, as a spreadsheet’s NETWORKDAYS does.
• Business days are Monday to Friday, nothing more. The tool knows no public holidays or other working weeks, so take holidays off yourself.
• A month is a calendar month, not 30 days. Between two dates, a month counts once the same day number comes round again. When the end month is too short for the start day, its last day counts, so 2025-01-31 to 2025-02-28 is 1 month, as is 2025-01-28 to 2025-02-28.
• When adding, months come first, then weeks and days. A year is 12 months, so 2024-02-29 plus 1 year clamps to 2025-02-28.
• Leap years follow the Gregorian rule: every fourth year, except century years not divisible by 400, so 2000 had a 29 February and 1900 didn’t. Dates before 1582 use the same rules carried backwards, the proleptic Gregorian calendar, so they won’t match records kept in the Julian calendar.
• An end date before the start makes every count negative, business days included. From 2024-03-10 to 2024-03-01 is -9 calendar days and -6 business days, or -5 without the end date, a Friday.
• Years run from 0000 to 9999, and each amount from -1000 to 1000. A result past either end shows That lands outside the years this tool covers, 0000 to 9999.

Questions

How many days are there between two dates?

Subtract the earlier date from the later one: from 14 October to 25 December 2026 is 72 days. That count leaves out the first day, so add 1 if both should count. In JavaScript, count in UTC so a daylight saving change can’t make a 23-hour day: (Date.UTC(2026, 11, 25) - Date.UTC(2026, 9, 14)) / 86400000 is 72.

How do I add days to a date?

Choose Add or subtract, set the start date and type the number in Days, or press a chip such as 90 days. In a shell, date -d '2026-10-14 + 90 days' +%F on Linux and date -j -v+90d -f %F 2026-10-14 +%F on macOS both print 2027-01-12.

How do I count business days between two dates?

Tick Count business days, Monday to Friday in Days between: the count includes both dates and skips Saturdays and Sundays. In Excel or Google Sheets, NETWORKDAYS(start, end) counts the same way and takes an optional list of holidays to leave out.

What is one month after January 31?

The last day of February: the 28th in a common year and the 29th in a leap year, because the date clamps to the end of the shorter month. JavaScript’s Date doesn’t clamp: setMonth(1) on 31 January 2025 rolls over to 3 March.