Two date calculations in one place
This tool has two modes. Days between dates counts the whole days separating a start date and an end date. Add/subtract days takes a start date and moves it forward or backward by a number of days to give a new date.
Both work on calendar days, so months of different lengths and leap years are handled correctly by the browser's date logic. Moving 30 days forward from 3 October 2026, for example, lands on 2 November 2026.
Everyday reasons to count days
Deadlines, notice periods, warranty windows, return policies, project plans, travel countdowns and payment terms are all expressed in days. Counting them on a paper calendar is easy to get wrong, especially across month ends.
The difference mode answers questions like how long until an event or how long a contract has run. The add mode answers "what date is 45 days after the invoice date" or "what date was 90 days before this one" when you enter a negative number.
How to use the date calculator
- Pick a mode with the two buttons at the top.
- In Days between dates, choose a Start date and an End date with the date pickers. Both begin on today's date. The Days between figure appears below.
- In Add/subtract days, choose the Start date and type the number of days. It starts at 30. Use a negative number to go backward.
- The resulting date is shown in year-month-day form.
As a check, from 31 January 2026 to 1 March 2026 is 29 days.
Details and limits
The difference is always shown as a positive number, even if the end date is earlier than the start date, so the tool does not tell you which date comes first. It counts the days that pass between the two dates, so the start day itself is not included in the total. If you need inclusive counting, add one.
The result is only a number of days. It does not break the gap into years, months and days, and it does not skip weekends or holidays. If the start date field is empty or cleared, the add mode may not produce a valid result, so pick a date first. For a years, months and days breakdown of someone's age, use the Age Calculator. For durations in hours and minutes, see the Time Calculator.