How to Add or Subtract Days, Months or Years from a Date

“What date is 90 days from now?” has a clean answer. “What date is one month from 31 January?” does not, because February is short.

Using the calculator

1. Enter the starting date and an amount.
2. Choose days, months or years, and add or subtract.
3. Read the result date.

Adding 90 days to 18 October 2026 gives 16 January 2027.

Months and years can overshoot

Months are not the same length. When the day number does not exist in the target month, the calculator rolls over into the next one, following how the browser’s date system works:

• 31 January 2026 plus 1 month gives 3 March 2026, not 28 February.
• 29 February 2024 plus 1 year gives 1 March 2025, since 2025 has no 29 February.

Many calendars and contracts instead clamp to the last day of the month, so check which rule applies. If you want the last day of the month, calculate from the 1st or subtract a day from the result.

Common uses

• Notice periods and payment due dates.
• Warranty or subscription expiry.
• Project milestones and follow-up reminders.

Check the rules that apply

Legal and financial deadlines often have their own rules for weekends, holidays and whether the first day counts. The calculator does plain calendar arithmetic, so use it as a starting point and confirm the rule that governs your deadline.

To see the gap between two dates instead, use the days between dates guide.

Frequently asked questions