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Time Calculator

Add or subtract durations in days, hours, minutes and seconds, or add time to a date and clock time to find the exact moment it lands on, weekday included.

Mode
First duration
Second duration
Empty boxes count as 0. A subtraction can give a negative result.

How to use the time calculator

Choose one of the two modes at the top of the form.

Two durations. Fill in the days, hours, minutes and seconds of the first duration, pick Add or Subtract, and fill in the second duration. Empty boxes count as zero, so for 2 hours 45 minutes you only need the Hours and Minutes boxes. The result is shown as days, hours, minutes and seconds, together with the same amount in total hours, total minutes and total seconds.

Date and time. The start date and time are filled in with your current local time; change them if you like. Pick Add or Subtract, enter a duration and press Calculate. You get the resulting date with its weekday and the clock time in both 24-hour and 12-hour form.

This tool works with lengths of time. If you want the time that passes between two clock times, such as a shift from 9:00 to 17:30, use the Time Duration Calculator instead.

How it works

Every duration is turned into seconds: a day is 86,400 seconds, an hour 3,600 and a minute 60. The two totals are added or subtracted, and the answer is split back into days, hours, minutes and seconds. Because the work is done in whole seconds, there are no rounding errors in the main result.

A subtraction may give a negative answer. It is shown with a minus sign, for example 1 hour minus 1 day 2 hours 30 minutes is −1 day, 1 hour, 30 minutes, 0 seconds (−25.5 hours).

Worked examples

  • 2 hours 45 minutes plus 1 hour 30 minutes is 4 hours 15 minutes. That is 4.25 hours, 255 minutes or 15,300 seconds.
  • You may type more than 59 minutes or more than 24 hours. 90 minutes plus 90 seconds becomes 1 hour, 31 minutes and 30 seconds.
  • Saturday, March 7, 2026 at 22:30 plus 1 day, 3 hours and 45 minutes is Monday, March 9, 2026 at 02:15 (2:15 AM).

Good to know

  • Daylight saving time is ignored on purpose. In the date and time mode every day is exactly 24 hours long. Adding 24 hours to noon always gives noon on the next day, even on a night when the clocks move. Real elapsed time across a clock change can differ by one hour, so adjust the result yourself if that matters.
  • Supported range. Dates run from the year 1 to the year 9999. Each box accepts whole numbers only; enter 1 hour 30 minutes rather than 1.5 hours.
  • Totals. Total hours are shown with up to six decimals and total minutes with up to four. Total seconds are always exact.

Frequently asked questions

How is this different from the Time Duration Calculator?

The Time Duration Calculator measures the time between two clock times, for example from 22:00 to 06:15. This Time Calculator does arithmetic with amounts of time: it adds or subtracts durations, or moves a date and time forward or backward by a duration.

Can the result be negative?

Yes. When you subtract a longer duration from a shorter one, the answer is shown with a minus sign. For example, 1 hour minus 1 day, 2 hours and 30 minutes is minus 1 day, 1 hour and 30 minutes, which is minus 25.5 hours.

Does adding time to a date take daylight saving time into account?

No. Each day is treated as exactly 24 hours, so adding 24 hours to 12:00 always gives 12:00 the next day. If the period crosses a clock change in your time zone, the real elapsed time may differ by one hour.

Can I enter decimal values such as 1.5 hours?

No, each box takes a whole number. Split the value instead: 1.5 hours is 1 hour and 30 minutes, and 2.25 days is 2 days and 6 hours. You can also type large numbers, such as 90 minutes, and the calculator will carry them over.