Add or Subtract Days Calculator
Enter a start date and a number of days to add or subtract, to instantly find the resulting date and which day of the week it falls on.
How the Add or Subtract Days formula works
Straightforward calendar arithmetic:
Resulting date = Start date ± number of days
The calculator handles month-length differences and leap years automatically, since it operates on actual calendar dates rather than a fixed 30-day approximation.
Step-by-step calculation
- Take the start date as the base.
- Add (or subtract, if the operation is subtraction) the entered number of days.
- The calendar automatically rolls over month and year boundaries correctly, including leap years.
- Read off the resulting date and its day of the week.
Worked example
Adding 45 days to July 26: the result lands on September 9 of the same year, accounting for July having 31 days and August having 31 days.
Frequently asked questions
Does this account for leap years automatically?
Yes — because the calculation works with real calendar dates rather than approximating months as 30 days, leap years and varying month lengths are handled correctly without any manual adjustment.
Can I add months or years instead of days?
This calculator works in days, which is the most precise unit — to add a certain number of weeks, just multiply by 7; for months or years, consider the exact number of days you want to shift by.