Time Add and Subtract Calculator
Add or subtract hours, minutes and seconds from a time.
Shifting a time by a duration
Adding a duration to a time, or subtracting one, comes up whenever you work with schedules and durations — what time is it three and a half hours from now, or ninety minutes before a start. This does that time arithmetic, handling the crossovers cleanly.
Enter a time and a duration to add or subtract.
Base-sixty and crossing midnight
Time arithmetic is fiddly for the same reason as duration calculation: time is not decimal, running in sixties for seconds and minutes, so you cannot simply add the digits — sixty-five minutes rolls over into an hour and five. Adding or subtracting across midnight is the other trap, where the result lands on a different day and the clock appears to go backward. Doing this by hand invites exactly these slips. The calculation handles the base-sixty carrying and the day boundary for you. It is the tool for working out arrival times, start times counted back from a deadline, when a process will finish, or any schedule question where you need to shift a clock time by a duration rather than work out how long something lasted.
Questions & answers
Why can't I just add the numbers to a time?
Because time runs in sixties, not tens, so sixty-five minutes rolls into an hour and five — and crossing midnight lands the result on another day.
What is it used for?
Working out arrival times, start times counted back from a deadline, or when a timed process will finish.
Is anything uploaded?
No. The calculation happens in your browser.