Add or subtract lengths of time. This free time calculator combines two durations in hours, minutes and seconds and shows the result in normalized form plus total hours, minutes, seconds and days.
Enter two durations in hours, minutes and seconds, then add or subtract them. Leave a box blank for zero. The result is normalized and also shown in single units.
Time is added by converting both durations to seconds, combining them, then converting back to hours, minutes and seconds. Subtracting a larger duration gives a negative result.
What This Time Calculator Does
Enter two durations in hours, minutes, and seconds, then add or subtract them. The result is shown in normalized hours-minutes-seconds form, plus totals in hours, minutes, seconds, and days alone.
How Durations Are Added
Both durations are first converted entirely to seconds, added together, and then converted back into normalized hours, minutes, and seconds – this avoids the common mistake of adding hours, minutes, and seconds columns independently without carrying over the excess.
For example, 1h 30m plus 45m equals 2h 15m 0s – the 30 and 45 minutes combine to 75 minutes, which carries an extra hour into the result.
Why Simple Column Addition Fails
Adding hours, minutes, and seconds as if they were separate decimal columns (like adding “30” and “45” to get “75” minutes without converting the excess to an hour) produces an incorrect, non-normalized result. Converting everything to a single unit (seconds) first avoids this entirely.
Subtracting Durations
Subtracting a larger duration from a smaller one produces a negative result, correctly indicating that Duration B exceeds Duration A rather than returning a nonsensical positive number.
Common Uses for This Calculator
This calculator is useful for combining video or audio clip lengths, adding up multiple exercise or activity sessions, totaling recorded work segments, or finding the difference between two elapsed-time measurements like lap times.
Why Time Doesn’t Use Base-10 Carrying
Ordinary decimal addition carries over at 10, but time carries over at 60 for seconds-to-minutes and minutes-to-hours, and at 24 for hours-to-days. This base-60 (and base-24) structure is exactly why time arithmetic needs its own carrying logic rather than behaving like ordinary decimal numbers.
A Subtraction Example With Borrowing
Subtracting 45 minutes from 1 hour 20 minutes requires borrowing, similar to decimal subtraction: 1h 20m minus 45m converts both to seconds (4800s minus 2700s = 2100s), which normalizes back to 35 minutes – not a simple “20 minus 45” column subtraction, which would go negative in the minutes column alone.
How to Use the Time Calculator
- Choose add or subtract.
- Enter Duration A and Duration B in hours, minutes, and seconds.
- Review the result, both normalized and as single-unit totals.
Working with clock times instead of durations? See our Hours Calculator.