Time Addition/Subtraction Calculator
Add or subtract hours, minutes, and seconds with automatic carrying and borrowing.
Enter up to 10 time values to get total duration in HH:MM:SS format.
Time arithmetic involves adding, subtracting, and converting between hours, minutes, and seconds. Unlike decimal numbers, time uses base-60 for seconds and minutes, and base-24 (or base-12) for hours — which requires special handling.
Key conversion factors:
- 1 hour = 60 minutes = 3,600 seconds
- 1 day = 24 hours = 1,440 minutes = 86,400 seconds
- 1 week = 7 days = 168 hours
Adding times: 3 hours 45 minutes + 2 hours 30 minutes: Minutes: 45 + 30 = 75 → 1 hour 15 minutes carry-over Hours: 3 + 2 + 1 = 6 Result: 6 hours 15 minutes
Subtracting times: 5 hours 20 minutes − 2 hours 50 minutes: Borrow 60 minutes: 5h 20min becomes 4h 80min 80 − 50 = 30 minutes 4 − 2 = 2 hours Result: 2 hours 30 minutes
Converting decimal hours to hours and minutes: 3.75 hours = 3 hours + (0.75 × 60) minutes = 3 hours 45 minutes
Converting minutes to decimal hours: 2 hours 20 minutes = 2 + (20/60) = 2.333… hours
Worked example — time sheet calculation: Start: 08:45, End: 17:15, Lunch break: 45 minutes Total elapsed: 17:15 − 08:45 = 8 hours 30 minutes Less lunch: 8h 30min − 45min = 7 hours 45 minutes = 7.75 decimal hours
24-hour vs 12-hour clock: 14:30 (24-hour) = 2:30 PM (12-hour) To convert 24-hour afternoon times: subtract 12 (14:30 − 12 = 2:30 PM)
Time zone arithmetic: UTC+2 is 5 hours ahead of UTC−3. If it is 10:00 in UTC−3, it is 15:00 in UTC+2.
Time arithmetic is used in payroll, scheduling, travel planning, sports timing, and project management.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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