Time Calculator
Add or subtract time durations in hours, minutes, and seconds.
Time 1
Time 2
Resulting Duration
Base 60 is why this is fiddly
Time arithmetic is awkward because it is not decimal. Minutes and seconds run in base 60 and hours in base 24, so carrying happens at 60 and 24 rather than 10. Adding 45 minutes to 2:30 gives 3:15, not 2:75 — the minutes overflow into an hour once they pass 60.
The reliable method is to convert everything to a single unit first. Turn both times into total seconds or total minutes, do ordinary arithmetic, then convert back. 2 hours 45 minutes becomes 165 minutes; add 90 and you have 255; divide by 60 to get 4 hours 15 minutes. This avoids every carrying error and is exactly what software does internally.
Decimal hours are the other common conversion, because payroll works in them: 7 hours 30 minutes is 7.5 hours, but 7 hours 15 minutes is 7.25, not 7.15. Divide the minutes by 60 rather than treating them as a decimal fraction. Crossing midnight needs care too — a shift from 22:00 to 06:00 is eight hours, which requires adding 24 to the end time before subtracting.
Frequently asked questions
How do I add hours and minutes?
Enter the hours, minutes, and seconds for each time value, then select Add or Subtract. The calculator handles carry-over automatically (e.g. 90 min = 1 hr 30 min).
Can I subtract time durations?
Yes. Switch to Subtract mode to find the difference between two time durations. The result is shown in hours, minutes, and seconds.
Does it handle days?
Yes. If the result exceeds 23:59:59, the overflow is shown as days plus remaining hours, minutes, and seconds.
How do I convert time into decimal hours?
Divide the minutes by 60 and add: 2 hours 45 minutes is 2 + 45/60 = 2.75 hours. Payroll and billing systems work in decimals, so writing 2.45 for 2 hours 45 minutes is one of the most common and expensive timesheet errors.