Add or Subtract Days from a Date

How it works

Adding days to a date walks the calendar forward by that many days:

result = start date + days

Enter a negative number of days to walk backward instead. The calculator converts the start date to a day number, adds the days, and converts back to a calendar date — so it crosses month boundaries (which are 28 to 31 days apart), year boundaries, and leap days correctly, without any manual carrying.

Leap years matter when the span crosses a February 29. A year is a leap year if divisible by 4, except centurial years, which must be divisible by 400 — so adding a day to 2024-02-28 lands on 2024-02-29 (a leap year), but the same step from 2026-02-28 lands on 2026-03-01.

This is useful for deadlines and waiting periods — a 30-, 60- or 90-day window from a start date, or counting back a number of days before an event.

Worked example

90 days after 2026-01-01 is April 1, 2026 (31 days in January + 28 in February + 31 in March = 90). Adding 1 day to 2026-12-31 rolls over to January 1, 2027. Subtracting — 7 days before 2026-01-01 — gives December 25, 2025.

Frequently asked questions

How do I add days to a date?

Enter the start date and the number of days to add: result = start + days. The calculator counts that many days forward on the calendar, rolling over months, years and leap days. 90 days after 2026-01-01 is April 1, 2026.

How do I subtract days from a date?

Enter a negative number of days. For example, −7 days from 2026-01-01 counts back a week to December 25, 2025. The calculation is the same; a negative count simply walks the calendar backward.

Does it handle month and year boundaries?

Yes. Because it works in whole days, it automatically carries across the end of a month (where lengths differ from 28 to 31 days) and the end of a year. Adding one day to 2026-12-31 gives 2027-01-01.

How are leap years handled?

The calculation includes February 29 whenever the span crosses one. A year is a leap year if divisible by 4, except centurial years, which must be divisible by 400. So adding a day to 2024-02-28 gives 2024-02-29, while the same step in the common year 2026 gives 2026-03-01.

What is this useful for?

Deadlines and waiting periods: a 30-, 60- or 90-day window from a contract or filing date, a return-by date, or counting a fixed number of days before an event. Enter the start date and the number of days, positive or negative.

Does it count business days?

No — it counts every calendar day, including weekends and holidays. A business-day offset would skip weekends and a country's holidays, which is a separate calculation.