Date Add / Subtract Calculator

Add or subtract any duration from a date

Choose a start date, enter an amount, select the unit (days, weeks, months, or years), and pick whether to add or subtract. The resulting date appears immediately. When adding months or years, the day is automatically clamped to the last valid day of the resulting month — so January 31 plus one month gives February 28 or 29 depending on whether it is a leap year, never an invalid date like February 31. Everything runs client-side; nothing is sent to any server.

Days and weeks use exact UTC day arithmetic. Month and year offsets follow calendar conventions, which is how most people intuitively think about "one month later". Use the days unit if you need a precise 30-day window instead.

FAQ

Why does adding one month to January 31 give February 28? There is no February 31, so the result is clamped to the last real day of February. This is the standard calendar convention used by most date libraries.

What is the difference between days and weeks? Weeks is a shortcut: entering 2 weeks is identical to entering 14 days. There is no "business week" logic — weekends are counted.

Can I enter negative numbers? Yes — a negative amount with "Add" selected is the same as a positive amount with "Subtract".