HomeDates & time
Add or subtract days
The date that is a number of days, weeks or months from a start date.
Quick answer
Adding days moves a date forward or back on the calendar, carrying over month ends and leap days. Formula: Result = start date ยฑ the number of days (weeks ร 7). 100 days after 1 January 2026 is Saturday, 11 April 2026.
Read the guide: How to find the number of days between two dates
Resulting date
Saturday, 11 April 2026
- As a number
- 2026-04-11
- Days from the start date
- 100
How is adding days to a date calculated?
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.
What is the formula for adding days to a date?
- 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
Can you show a worked example of adding days to a date?
1 January 2026 plus 100 days: January has 31 days, February 28, March 31, so 100 days later is 11 April 2026, a Saturday.
What date is a number of days after 1 January 2026?
Start date 1 January 2026, adding the days shown.
| Days added | Resulting date |
|---|---|
| 30 | Saturday, 31 January 2026 |
| 60 | Monday, 2 March 2026 |
| 90 | Wednesday, 1 April 2026 |
| 100 | Saturday, 11 April 2026 |
| 180 | Tuesday, 30 June 2026 |
| 365 | Friday, 1 January 2027 |
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.