Add or Subtract Time

Add / Subtract Time from a Date

Please select a valid start date and time.

Add or Subtract Time from Any Date

Need to know what date falls 90 days from now? Or when a 6-month subscription that started today will expire? Our add/subtract time calculator lets you add or remove any combination of years, months, days, hours, minutes, and seconds from any starting date and time — and shows the exact result instantly.

How It Works

Select your starting date and time, choose whether to add or subtract, then enter the duration components. Years and months are handled calendar-aware (adding one month to January 31 gives the last day of February). Days, hours, minutes, and seconds are converted to an exact millisecond delta for precision.

Practical Uses

  • Project planning: Add the project duration to a kick-off date to find the delivery deadline.
  • Subscription expiry: Add 1 year (or 12 months) to a sign-up date to find renewal date.
  • Warranty end dates: Find when a 2-year product warranty expires from the purchase date.
  • Legal deadlines: Add statutory response periods (e.g., 30 days) to a notice date.
  • Cooking and science: Add precise durations to a start time to find process completion.
  • Age milestones: Subtract years from today to find a past birth year or anniversary.

Why Calendar-Aware Month Arithmetic Matters

Adding "one month" is not the same as adding 30 days. If you add one month to March 31, the result is April 30 (not May 1), because April only has 30 days. This calculator uses proper calendar arithmetic for months and years, mirroring how humans understand time — not just fixed-length approximations.

Frequently Asked Questions

What happens if I add months past the end of a shorter month?
JavaScript's Date object handles this by rolling over: adding 1 month to January 31 gives February 28 (or 29 in a leap year), not March 2 or 3. This matches most real-world expectations for contract and subscription dates.
Can I combine years, months, and days in one calculation?
Yes. Fill in any combination of fields — leave unused ones as 0. The calculator applies years and months first (calendar-aware), then adds the days, hours, minutes, and seconds as a fixed duration.
Does this account for leap years?
Yes. Adding 1 year to February 28 in a non-leap year gives February 28 of the following year. If the following year is a leap year and you started on Feb 28, you'll get Feb 28 — not Feb 29.
How far in the future or past can I calculate?
JavaScript's Date object supports dates from 100 million days before to 100 million days after January 1, 1970 — far beyond any practical use case.
Is the result shown in my local time zone?
Yes. All inputs and outputs use your browser's local time zone. The calculation is entirely local — no server calls are made.