How to calculate time duration
The basic method is to subtract the start time from the end time, giving you the elapsed span in minutes, then convert that into hours and minutes. A period from 09:15 to 17:45 is 8 hours 30 minutes, or 510 total minutes. This calculator performs both steps and also shows the decimal hours figure that payroll systems expect.
Crossing midnight / overnight times
When a period crosses midnight the end time is earlier than the start time on the clock. The calculator detects this and adds 24 hours, so 22:00 to 06:00 is counted as an 8-hour span rather than a negative number. The result is labelled overnight when this happens.
Decimal hours
Decimal hours express minutes as a fraction of an hour, which is what most payroll and timesheet systems expect. To convert manually, divide the minutes by 60 and add the result to the hours: 8 hours 30 minutes is 8 + 30/60 = 8.50 decimal hours. This calculator shows hours:minutes, total minutes and decimal hours side by side.
Adding and subtracting time
Switch to the Add or subtract time mode to shift a starting time forward or backward. Enter the starting time, choose Add or Subtract, then enter the hours and minutes to apply. The result wraps around the 24-hour clock, so 23:30 plus 2 hours gives 01:30. This is handy for working out finish times, deadlines and time-zone shifts without counting on your fingers.
Worked examples
- Daytime span 09:15 to 17:45 = 8h 30m, 510 total minutes, 8.50 decimal hours.
- Overnight span 22:00 to 06:00 = 8h 0m, 480 total minutes, 8.00 decimal hours.
- Short span 13:20 to 14:05 = 0h 45m, 45 total minutes, 0.75 decimal hours.
- Add time 14:30 + 2h 45m = 17:15.
- Subtract across midnight 01:15 − 3h 00m = 22:15 (wraps back to the previous day).
FAQs
- How do I calculate the time duration between two times?
- Subtract the start time from the end time to get the elapsed span in minutes, then convert to hours and minutes. This calculator does both steps instantly and shows the total minutes and decimal hours too.
- How are overnight times handled?
- If the end time is not later than the start time, the calculator treats the period as crossing midnight and adds 24 hours. So 22:00 to 06:00 is counted as 8 hours, not a negative number.
- What are decimal hours?
- Decimal hours express minutes as a fraction of an hour, which is what most payroll systems expect. 8 hours 30 minutes becomes 8.50 decimal hours, not 8.30.
- How do I add or subtract time from a starting time?
- Use the Add or Subtract mode. Enter a starting time, then the hours and minutes to add or take away. For example, 14:30 plus 2 hours 45 minutes gives 17:15. The result wraps around the 24-hour clock.
- Is anything I type stored?
- No. The calculator runs entirely in your browser. Nothing is sent to a server or saved between visits.