Date Calculator
Add or subtract days from any date with this free date calculator. Enter a start date and a number of days to get the resulting date and weekday.
About this tool
Deadlines, travel plans, project schedules and pregnancy due dates all involve counting days on a calendar. Doing it by hand means flipping through months, remembering which have 30 or 31 days, and watching out for leap years. It is slow and easy to get wrong by a day.
Our free date calculator does it perfectly in one click. Pick a start date, enter how many days to add or subtract, and the tool returns the exact resulting date along with the day of the week.
How to use
Choose the start date with the date picker, type the number of days, and select whether to add or subtract them. Press Calculate Date and the answer appears with the full date and weekday, for example Saturday, 31 January 2026.
Month lengths and leap years are handled automatically, so 28 February plus 3 days in a leap year correctly lands on 2 March.
The math behind it
The tool converts your start date into a calendar date object and then shifts it by the number of days you entered. Adding days rolls months and years forward naturally: 31 days after 1 January is 1 February. Subtracting works the same way in reverse.
Leap years follow the standard rule: a year divisible by 4 is a leap year, except centuries, which must also be divisible by 400. So 2024 and 2028 are leap years, but 2100 is not.