Add or Subtract Days
Add days to a date or subtract days from a date — useful for deadlines, due dates, travel dates and schedules.
How the calculation works
The calculator moves forward or backward by whole calendar days from the start date. It crosses month and year boundaries automatically, and leap days are counted exactly — so adding days across February in a leap year gives a different answer than in a common year, as it should.
The start date itself is not counted: adding 1 day to 1 January gives 2 January, and adding 0 days gives the start date back unchanged.
Worked example
1 January 2026 plus 100 days is 11 April 2026, a Saturday. Counting it out: 30 days remain in January after the 1st, February 2026 has 28 days, and March has 31 days — that is 89 days to 31 March. Eleven more days into April brings the total to 100 and lands on 11 April.
Frequently asked questions
Can I add more than a year?
Yes. You can add or subtract up to 36,500 days — about 100 years. For longer spans, split the calculation into steps.
Is the start date counted?
No. Adding 1 day to 1 January gives 2 January. If you need to count the start date as day one — for example, a 7-day course starting on a Monday — add 6 days instead of 7 to find the last day.
Does it handle leap years?
Yes. Leap days are counted exactly. Adding 60 days to 1 January 2024 lands on 1 March 2024, because February 2024 has 29 days; adding 60 days to 1 January 2023 lands on 2 March 2023.
What is this useful for?
Common uses are deadlines ("90 days from today"), due dates, return windows, travel planning, and working out when a notice period or subscription ends.
Can I subtract to a date in the past?
Yes — choose "Subtract days". The calculator works with dates from year 1 onwards on the Gregorian calendar.
Related tools
- Days Between Dates — count the days between any two dates.
- Days Until — Countdown — count down to a future date.
- Age Calculator — how old are you, in years, months and days?
- Day of the Week — find the weekday of any date.