Add or Subtract Time Calculator

The on-page calculator works in hours and minutes for both the start time and the duration. There is no separate seconds box in the tool, though the underlying engine and the JSON API do accept seconds if you need that precision.

Use the Add and Subtract toggle above the result. Subtract removes the duration from the start time, so 02:00 minus 5 hours gives 21:00 on the previous day, with the day shift shown for you.

Yes. Adding past 24:00 rolls into the next day and subtracting before 00:00 rolls into the previous day. The result labels the shift, for example next day or previous day, so you are never left guessing which day it lands on.

Yes. The duration hours field takes any whole number, so 9:00 plus 50 hours returns 11:00 with a 2 days later label. It counts every whole day crossed and reports the final time of day.

Both input and output use the 24 hour clock, so 1 PM is entered and shown as 13:00. Working in 24 hour time removes any AM and PM ambiguity around noon and midnight.

No. This is a pure clock-arithmetic tool that works on a time of day, not on real calendar dates, so it never adds or removes an hour for daylight saving and has no concept of time zones. Every hour is treated as exactly 60 minutes.

Not the date itself. It reports the resulting time of day plus a whole-day offset, such as next day or 2 days earlier, but it does not compute a specific calendar date. To add a duration to a full date, use a date-based calculator instead.

The result is shown as HH:MM with a leading zero when needed, for example 02:45. If seconds are supplied through the API, the format extends to HH:MM:SS. A day label is added underneath only when the time crosses midnight.

Yes. All of the arithmetic happens in your browser and nothing is uploaded or stored. You can even use the calculator offline once the page has loaded.