Add / Subtract Days
Find a future or past date
About This Calculator
Adding or subtracting days from a date finds a future or past date, accounting for month lengths and leap years automatically. This is essential for calculating deadlines (30-day payment terms, 90-day return policies), scheduling future appointments, planning project timelines, and determining when contracts expire.
Formula
Future date = Start date + N days
Past date = Start date − N days
For business days: skip Saturdays, Sundays, and holidays
30 days ≠ 1 month (months have 28-31 days)
Example Calculation
Contract signed March 16, 2026 — when does a 90-day term expire?
- March 16 + 90 days
- March: 31-16 = 15 days remaining
- April: 30 days (total: 45)
- May: 31 days (total: 76)
- June: need 90-76 = 14 more days → June 14
90-day term expires: June 14, 2026
Common Deadline Calculations
| From Date | + 30 days | + 60 days | + 90 days | + 1 year |
|---|---|---|---|---|
| January 15 | February 14 | March 16 | April 15 | January 15 (next year) |
| March 1 | March 31 | April 30 | May 30 | March 1 (next year) |
| November 1 | December 1 | December 31 | January 30 | November 1 (next year) |
Frequently Asked Questions
What is the difference between 30 days and 1 month?
30 calendar days is a fixed number of days (30 exactly). 1 month can be 28, 29, 30, or 31 days depending on the month. A payment due '30 days from March 1' is due March 31. A payment due '1 month from March 1' is due April 1.
How do I calculate a date 6 months from now?
Add 6 to the current month number, adjusting the year if needed. If the resulting month doesn't have the same day (e.g., adding 6 months to August 31 → February 31 which doesn't exist), use the last day of the target month instead.
What happens with leap years when adding months?
Adding 1 year to February 28 in a leap year stays at February 28 in the next year. Adding 1 year to February 29 gives February 28 in non-leap years. Always verify dates near February for leap year edge cases.
How do banks calculate interest periods?
Most banks use actual calendar days. A '30-day' Treasury bill is literally 30 calendar days. Mortgages use the Actual/360 or 30/360 day count convention. Make sure you know which convention applies when calculating financial deadlines.