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âž• Add/Subtract Days from a Date
Quickly find a date in the past or future.
How adding and subtracting dates works
This tool takes your start date and shifts it forward or backward by the amount and unit you choose. When adding or subtracting months or years, it automatically adjusts for month length — for example, adding one month to January 31 lands on the last valid day of February rather than an invalid date.
Why this is trickier than it looks
- Days and weeks are straightforward — each day always represents the same fixed unit of time.
- Months vary in length (28–31 days), so "add 1 month" means "move to the same day next month," not "add 30 days."
- Years must account for leap years — adding a year to February 29 requires special handling since not every year has a February 29.
Worked example: Starting from January 15, 2026 and adding 3 months gives April 15, 2026. Subtracting 10 days from that same start date gives January 5, 2026.
Common uses
Due datesAdd 30/60/90 days to an invoice or contract date to find the payment deadline.
Return windowsAdd a return period (e.g. 14 or 30 days) to a purchase date.
Planning aheadAdd weeks or months to today's date to schedule follow-ups or renewals.
Looking backSubtract days or months to find out what date something happened relative to today.
Frequently asked questions
What happens if adding a month lands on an invalid day?
The calculator automatically rolls back to the last valid day of the resulting month — for example, adding a month to January 31 gives February 28 (or 29 in a leap year).
Can I use negative numbers in the amount field?
You don't need to — use the "Direction" dropdown to choose Add or Subtract, and enter a positive number for the amount.
Does this account for leap years automatically?
Yes, all date math uses standard calendar rules, so leap years are handled without any extra input from you.