HomeDates & time
Add or subtract days
The date that is a number of days, weeks or months from a start date.
Quick answer
Enter a start date and a number of days. 100 days after 1 January 2026 is Saturday, 11 April 2026.
Resulting date
Saturday, 11 April 2026
- As a number
- 2026-04-11
- Days from the start date
- 100
How it works
Adding days moves along the calendar one day at a time, crossing month ends and leap days correctly.
Adding months keeps the same day of the month. If that day does not exist (31 March plus one month), you get the last day of the shorter month.
Useful for notice periods, due dates, warranties and course end dates.
The formula
- Result = start date ยฑ the number of days (weeks ร 7)
- For months and years the day of the month is kept, or the last day of a shorter month
A worked example
1 January 2026 plus 100 days: January has 31 days, February 28, March 31, so 100 days later is 11 April 2026, a Saturday.
Common questions
How do I find the date 90 days from today?
Set the start date to today, choose Add and enter 90 days.
What is 31 January plus one month?
The last day of February, because February has no 31st.
Does it skip weekends?
No, it counts calendar days. The working days calculator handles weekdays.
Can I go back in time?
Yes. Choose Subtract.