Time Calculator – Add or Subtract Time

How to Add or Subtract Time

The time calculator takes a starting time, a duration to add or subtract, and returns the resulting time on a 24-hour clock. It handles midnight overflow automatically — adding 3 hours to 23:00 correctly returns 02:00, not an error.

Select your starting hour and minute, choose whether to add or subtract, enter the duration, and the result appears instantly.

Examples

How the Calculation Works

The calculator converts everything to minutes, performs the addition or subtraction, then wraps the result using modulo 1440 (the number of minutes in a day). This ensures the result always stays within a valid 24-hour range regardless of how large or small the input is.

For example: 23:00 is 1380 minutes. Adding 3 hours (180 minutes) gives 1560 minutes. 1560 mod 1440 = 120 minutes = 02:00.

Common Uses

Shift scheduling: A shift starting at 22:00 lasting 8 hours ends at 06:00 the next day. Manual calculation across midnight is error-prone — this calculator handles it automatically.

Meeting planning: A 1.5-hour meeting starting at 15:45 ends at 17:15. Quickly check whether it fits before the end of the working day.

Travel and flights: A 14-hour flight departing at 20:00 arrives at 10:00 the next day in the same timezone.

Cooking: If something needs 2 hours 45 minutes and you want it ready at 19:30, subtract to find the start time: 16:45.

Frequently Asked Questions

How do you add hours and minutes to a time?

Convert everything to minutes from midnight, add the duration, then convert back to hours and minutes. This calculator does it automatically.

What happens when the result goes past midnight?

The calculator wraps automatically. Adding past 23:59 rolls over to 00:00. Subtracting below 00:00 wraps back to 23:59.

Does the calculator use a 12-hour or 24-hour clock?

24-hour clock. Enter hours from 0 (midnight) to 23 (11 PM). The result is displayed in HH:MM format.

Can I add more than 24 hours?

Yes. The calculator supports durations longer than 24 hours and wraps the result correctly.

How do I find an end time from a start time and duration?

Set the operation to Add, enter your start time and duration. The result is your end time.