DATE & DURATION

Add Time Calculator

Enter a starting date and time, choose a duration to add, and get the resulting date and time.

Add a duration to a date and time

Enter a starting date and time, a time zone, an amount and a unit (seconds, minutes, hours, days or weeks), and the tool returns the resulting date and time. This is useful for working out a deadline, an expiry time, or a follow-up date without counting on a calendar.

Exact time vs calendar days

Seconds, minutes and hours add an exact amount of elapsed time. Days and weeks add calendar days in the time zone you choose and keep the same clock time, even across a daylight saving change, the way a person scheduling “this time next week” would expect. If the result would land in a gap created by clocks moving forward, the tool moves it forward by the size of the gap and tells you.

Want the background? Read our comprehensive guide: Time Zones and DST for Developers.

How to use this tool

Enter the starting date and time, or select Use current time.
Choose the time zone.
Enter the amount to add and choose the unit.
Select Add time to see the resulting date and time.

Examples

Adding a calendar unit (weeks) and an exact-time unit (hours).

Add 1 week

2026-09-21 12:00 UTC + 1 week

Result: 2026-09-28T12:00:00.000Z

Add 36 hours

2026-09-21 12:00 UTC + 36 hours

Result: 2026-09-23T00:00:00.000Z

Add 90 seconds

2026-09-21 12:00 UTC + 90 seconds

Result: 2026-09-21T12:01:30.000Z

Frequently Asked Questions

Does adding days keep the same time of day?

Yes. Adding days or weeks keeps the clock time and moves the calendar date, even when a daylight saving change happens in between.

What happens if adding hours crosses a daylight saving change?

Adding hours always adds an exact amount of elapsed time, so the result may show a clock time that is one hour different from what you might expect, because the offset changed in between.

Can I add a fractional number of hours?

Yes for seconds, minutes and hours. Days and weeks must be whole numbers; use hours if you need a fraction of a day.

How do I subtract time instead?

Use the Subtract Time Calculator, which works the same way but moves backward from the starting date and time.