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Add / subtract to a date

Choose a date, then add or subtract years, months, weeks and days to find the resulting date.

How Add or subtract dates works

Add or Subtract Dates lets you shift any date forward or backward by a combination of years, months, weeks and days. Type your starting date, enter the amounts to add (or check the subtract option), and the resulting date is computed immediately in your browser. No data leaves your device, and the arithmetic works offline once the page is cached.

Under the hood the calculation applies each unit in order: years first, then months, then weeks, then days. This ordering matters when months have different lengths. Adding one month to 31 January, for instance, lands on 28 February (or 29 in a leap year) rather than an invalid date. Adding years before months means that 'add one year and one month to 31 January 2023' becomes 28 February 2024, matching the calendar convention most people expect.

Written by Bastien Sulyan

How to use Add or subtract dates, step by step

  1. Enter your starting date.
  2. Type the number of years, months, weeks and days you want to add.
  3. Toggle the subtract option if you want to move backward in time instead.
  4. Read the resulting date displayed below the inputs.
  5. Adjust any value and the result updates at once.

Common use cases

  • A contractor needs to find the date 90 days after project kick-off to set a review milestone.
  • A subscription renews every 6 months from a specific start date; calculate the next renewal date.
  • A warranty expires 2 years and 3 months after purchase; find the exact expiry date.
  • A doctor prescribes a 14-day course of treatment starting on a given day; determine the last day of the course.

Frequently asked questions

What order does the tool apply years, months, weeks and days?

Years are added first, then months, then weeks, then days. This order is important for month-end dates. Adding one month to 31 January gives 28 or 29 February, not an overflow into March. Weeks and days are added on top of that result as a flat number of calendar days.

Can I subtract instead of add?

Yes. Enable the subtract toggle (or enter a negative number in the relevant field, depending on the interface). The same arithmetic runs in reverse, walking the calendar backward by the specified amounts.

How does the tool handle adding months to a month-end date?

When the resulting month has fewer days than the start date's day-of-month, the tool clamps to the last valid day of the target month. Adding one month to 31 March gives 30 April, not 1 May.

Are the dates I enter transmitted anywhere?

No. The start date and the increment values you type stay inside your browser tab. The calculation is a few lines of date arithmetic that run locally; there is no network request of any kind.

Can I chain multiple additions, for example 'add 6 months then subtract 3 days'?

Fill in all fields at once: set months to 6 and days to -3 (or use a combined add/subtract field for days). The tool applies all units in the defined order in a single pass, so you do not need multiple steps.

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