Quick answer
Pick “Days between dates”, enter a start and end date and you get the number of days, weeks, years–months–days and working days. For example, 1 January 2026 to 1 January 2027 is 365 days, and October 2026 has 22 Monday-to-Friday working days.
What can a date calculator do?
One tool for everyday date maths: count the days to a deadline, the working days in a period, add 30, 45 or 90 days to find a due date, add months or years, or work out an exact age. Calculations use calendar days, so time zones and daylight saving never shift the result, and leap years and short months are handled correctly.
How to use it
- 1
Choose “Days between dates”, “Add / subtract” or “Age”.
- 2
Pick dates with the date picker or type them; “Today” fills in the current date.
- 3
For differences, tick “Include the end date” when both ends count (Monday to Friday leave is 5 days), and “Saturday is a working day” for a six-day week.
- 4
For adding, choose Add or Subtract, the amount and the unit (days, weeks, months, years, working days), or use the 7–180 day shortcuts.
- 5
Copy the result into your email, plan or contract.
Days in each month
| Month | Days | Note |
|---|---|---|
| Jan, Mar, May, Jul, Aug, Oct, Dec | 31 | Seven long months |
| Apr, Jun, Sep, Nov | 30 | |
| Feb | 28 or 29 | 29 in leap years: divisible by 4, except centuries not divisible by 400 |
Adding months to month-end dates
| Start | Operation | Result |
|---|---|---|
| 31 Jan 2026 | + 1 month | 28 Feb 2026 |
| 31 Jan 2024 | + 1 month | 29 Feb 2024 (leap year) |
| 31 Mar 2026 | + 1 month | 30 Apr 2026 |
| 29 Feb 2024 | + 1 year | 28 Feb 2025 |
Examples
Counting leave
Monday 26 to Friday 30 October 2026 with “Include the end date” ticked: 5 days, all working days.
90-day due date
A contract signed on 21 October 2026 with 90-day terms is due on Tuesday 19 January 2027.
Five working days
Five working days after Friday 23 October 2026 is Friday 30 October 2026.
Exact age
Born 15 August 1990, on 21 October 2026: 36 years 2 months 6 days, turning 37 on 15 August 2027.
Common problems
- The result is one day short.
- By default the tool counts the gap between dates, like a subtraction. Tick “Include the end date” for leave or trips.
- Working days don't match payroll.
- Weekends are excluded but public holidays are not, because they vary by country and some follow the lunar calendar.
- 31 Jan + 1 month gave 28 Feb.
- That's the standard rule (Excel and banks use it too). Use the Days unit to add exactly 30 days instead.
Month arithmetic
Adding a month keeps the day of the month where possible and clamps to the last day otherwise, so 31 January plus one month is the end of February. The years–months–days breakdown uses the same rule, which is why 31 January to 1 March is 1 month 1 day.
Working days
Working days exclude Sundays and, unless you tick the six-day week option, Saturdays. Public holidays are not removed automatically; subtract the ones that fall inside your period.
Glossary
- Date difference
- The number of days from the start date to the end date, not counting the start (like a subtraction).
- Working day
- Any day except Saturday and Sunday (or only Sunday in a six-day week), before removing public holidays.
- Leap year
- A 366-day year with 29 February: divisible by 4, except centuries not divisible by 400.
Frequently asked questions
How many days until a date?
Use “Days between dates” with today as the start (it is filled in for you) and pick the end date.
Are public holidays excluded?
No, only weekends. Subtract holidays yourself.
What's the difference between adding a month and 30 days?
Adding a month keeps the day of the month (15 Jan → 15 Feb); 30 days counts calendar days (15 Jan → 14 Feb).
What about birthdays on 29 February?
In non-leap years the tool uses 28 February.
Is anything stored?
No. All calculations run in your browser.
Ratings and comments
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