Date Calculator — add or subtract years, months, days

How it works

This shifts a date by a mix of units:

result = start date + years + months + weeks + days

The years and months are applied first, then the weeks and days. Enter negative numbers to go back in time. Because it works on the calendar, it handles month lengths and leap years automatically — a year is a leap year if divisible by 4, except centurial years, which must be divisible by 400.

Adding months clamps to the end of a shorter month: one month after January 31 is February 28 (or February 29 in a leap year), since there is no February 31. Weeks and days are simple 7-day and 1-day steps that roll over month and year boundaries.

This differs from a plain add-days calculation: adding "3 months" lands on the same day number three months later, which is not the same as adding 90 days.

Worked example

3 months and 2 weeks after 2026-01-01 is April 15, 2026 (January 1 + 3 months = April 1, + 2 weeks = April 15). One year after is January 1, 2027. Going back 6 months from January 1, 2026 lands on July 1, 2025.

Frequently asked questions

How do I add months to a date?

Enter the start date and the number of months. The calculator moves to the same day number that many months later, clamping to the end of the month when needed — so one month after January 31 is February 28 (or 29 in a leap year). Use a negative number to subtract months.

What is the difference between adding months and adding days?

Adding a month keeps the day number and moves the month, so its length in days varies (28 to 31). Adding days is a fixed step. Three months after January 1 is April 1 (90 days), while three months after, say, February 1 is May 1 (89 days). Use whichever matches your need.

How do I subtract time from a date?

Enter negative numbers in any of the year, month, week or day fields. For example, −6 months from January 1, 2026 gives July 1, 2025. You can mix positive and negative units.

How are leap years handled?

Automatically. Adding a year to February 29 lands on February 28 in the following common year (there is no February 29 then), and day/week steps include February 29 whenever the span crosses one. The leap-year rule is divisible by 4, except centuries not divisible by 400.

In what order are the units applied?

Years and months are applied first (as calendar shifts, with month-clamping), then weeks and days are added as plain 7-day and 1-day steps. This matches how people usually describe an offset like "one year and ten days from now."

What is the total days figure?

It is the whole number of calendar days between the start date and the result — a handy check on how far the shift moved, since a month or year is a variable number of days.