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Date Add Subtract Calculator

Add or subtract days, weeks, months, or years from any date.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Choose your start date in the date field (it defaults to today).
  2. 2.Select Add or Subtract, type the amount, and pick the unit: days, weeks, months, or years.
  3. 3.Read the result date and its weekday instantly below, with no button to press.

About Date Add Subtract Calculator

This date add subtract calculator returns the exact result date the moment you type. Pick a start date, choose Add or Subtract, enter an amount, and select days, weeks, months, or years. The answer, including the weekday, updates live with no button to press, so you can see at a glance what date lands 30, 90, or 180 days out or back.

The math is calendar-correct, not a naive multiplication. When you add or subtract months and the target month has no matching day, the result is clamped to the last valid day of that month, exactly like the date-fns addMonths rule. So January 31 plus one month is February 28 (February 29 in a leap year), not March 3, and March 31 minus one month is February 28. Adding years follows the same clamp: February 29, 2020 plus one year becomes February 28, 2021, because 2021 is not a leap year. Weeks are handled as exact seven-day multiples, so 2 weeks is always 14 days, and day and week math roll across month and year boundaries and every leap year automatically.

Leap years use the full Gregorian rule (divisible by 4, except centuries unless divisible by 400), so February lengths and day counts are always right. You can subtract far enough to move into past centuries, and the tool keeps the calendar consistent instead of drifting.

Alongside the full date and weekday, the tool shows a compact summary line, such as 2026-07-06 + 30 days = 2026-08-05, so you can copy the ISO result straight into a spreadsheet, calendar entry, or ticket. Changing the amount or unit recalculates immediately, which makes it easy to compare a 30-day, 60-day, and 90-day horizon in seconds.

Common uses: find a delivery or shipping deadline a set number of calendar days out, calculate a billing or subscription renewal one, three, or twelve months after a signup date, work out a contract end date years ahead, count down to an appointment or a warranty expiry, or back-date a document. Because the result shows the weekday, you can immediately tell whether a due date falls on a weekend and adjust before it becomes a problem.

Everything runs in your browser. The date you enter never leaves your device and nothing is uploaded or stored, so it is safe for private schedules and confidential contract dates. There is no signup and no limit on how many calculations you run. If you need the number of days between two known dates instead of adding to one, use a days-between calculator; to work out an age or an anniversary from a birth date, use an age calculator. For deadlines that must skip weekends, pair this with a business-days calculator.

Frequently asked questions

What is 30 days from today?
Set the start date to today, choose Add, enter 30, and pick Days. The tool shows the exact date 30 calendar days from now, including the weekday, updated the moment you type.
How does adding months handle the end of the month?
If the target month has no matching day, the result is clamped to that month's last day, the same rule date-fns uses. So January 31 plus one month is February 28, or February 29 in a leap year, never March 3.
How are weeks calculated?
One week is treated as exactly 7 days, so the amount you enter is multiplied by 7 and added or subtracted as calendar days. Two weeks is always 14 days, rolling across month and year boundaries correctly.
Can I subtract to go back in time?
Yes. Choose Subtract and the tool counts backward from your start date across months, years, and leap years. You can back-date documents or find a date that was a given number of days, weeks, months, or years ago.
How are leap years handled?
The calculator uses the full Gregorian leap-year rule, so February has 29 days when the year is divisible by 4 but not by 100 unless also by 400. February 29 plus one year clamps to February 28 in a non-leap year.

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