Add or Subtract Days Calculator
Add or subtract days, weeks, months, or years from any date and see the resulting date and weekday — runs 100% in your browser with no upload.
2026-08-07
Friday
🔒 Calculated in your browser — nothing is uploaded.
What this tool does
Pick a start date, type how much to shift it, and choose whether the amount is counted in days, weeks, months, or years. The tool instantly shows the resulting date along with its weekday, so you can answer questions like "what date is 90 days from today?" or "which day of the week is three weeks before this deadline?" without counting on a calendar. Enter a negative amount to move backwards in time and a positive amount to move forwards. Everything updates live as you type, so you can nudge the number up and down to explore different scenarios instantly.
How the shift is calculated
Days and weeks are added as a plain count of calendar days, where one week is seven days. Months and years are calendar aware: adding one month to January 31 lands in the next month at the same day when it exists, and rolls forward when it does not — for example January 31 plus one month becomes March 2 in a leap year, because February has no 31st. Adding a year to February 29 similarly rolls to March 1 in a non-leap year. This matches how JavaScript's own date arithmetic behaves, giving predictable, deterministic results for the same inputs every time.
Frequently asked questions
How do I subtract instead of add?
Type a negative amount. For example, entering -30 with the unit set to Days gives the date 30 days before your start date, and -1 with the unit set to Years gives the same day one year earlier.
Why does adding one month to January 31 skip to March?
February has no 31st day, so the calculation rolls the overflow forward. January 31 plus one month becomes March 2 in a leap year (or March 3 in a common year). This calendar-aware behaviour keeps month and year math consistent and predictable.
Is my date sent to a server?
No. The date and amount you enter never leave your device. The resulting date and weekday are calculated entirely in your browser with JavaScript — nothing is uploaded, logged, or stored.