Time Duration Calculator
Add or subtract two durations in hours, minutes, and seconds and see the normalized result.
First duration
Second duration
Runs entirely in your browser. Nothing you type is uploaded anywhere.
How to use this tool
Pick whether you want to add the two durations together or subtract the second from the first using the toggle at the top. Then enter each duration in the hours, minutes, and seconds boxes. You can leave any box blank and it will count as zero. Press Calculate and the time duration calculator will add or subtract the two values and show the normalized answer in clean hours:minutes:seconds notation, plus a plain words version and the total in seconds. Use Copy result to grab the answer, or Clear to start over.
How the time math works
add: result = first total + second total
subtract: result = first total - second total
normalize: hours = result / 3600, minutes = (result % 3600) / 60, seconds = result % 60
Time notation math is easiest when you first turn each duration into a single number of seconds. Once both durations are plain seconds, you can simply add or subtract them. To show a readable answer the tool then converts the total back into hours, minutes, and seconds, carrying any overflow. For example 90 seconds becomes 1 minute and 30 seconds, and 75 minutes becomes 1 hour and 15 minutes. This is how you sum time intervals without losing track of the carries between units.
A real example
Say you worked a morning shift of 3 hours 45 minutes and an afternoon shift of 2 hours 50 minutes, and you want to add hours and minutes together. The first duration is (3 * 3600) + (45 * 60) = 13,500 seconds. The second is (2 * 3600) + (50 * 60) = 10,200 seconds. Adding them gives 23,700 seconds. Normalizing: 23,700 / 3600 = 6 hours, with 1,500 seconds left over, which is 25 minutes and 0 seconds. So the total is 6 hours 25 minutes, shown as 6:25:00.
Common questions
Can I subtract a longer time from a shorter one?
Yes. If the second duration is larger than the first, the result will be negative and the tool shows a minus sign in front of the normalized time so you can see the difference clearly.
Do I have to fill in all three boxes?
No. Any box you leave blank is treated as zero, so you can enter just minutes, just hours and minutes, or all three units in any combination.
What does normalized mean here?
Normalized means the answer is carried into proper units, so 90 seconds is shown as 1 minute 30 seconds rather than 0 minutes 90 seconds. Minutes and seconds always stay between 0 and 59.
Can it handle large durations over 24 hours?
Yes. The hours field is not capped at 24, so you can sum time intervals that add up to many days worth of hours and the result simply shows the full hour count.
Does this work offline?
Once the page is loaded the calculation runs fully in your browser with no server, so it keeps working even if your connection drops.