Time Duration Calculator
Add or subtract hours, minutes and seconds.
Good to know. 90 minutes is 1:30, or 1.5 hours. Never 1:90. Time counts in sixties, which is nobody’s favourite.
How it works
In plain words
Convert both durations to seconds, add or subtract them, then convert back into hours, minutes and seconds.
The formula
seconds = h × 3600 + m × 60 + s result = first ± second
Worked example
2 h 45 min plus 1 h 30 min: 9,900 + 5,400 = 15,300 seconds, which is 4:15:00, or 4.25 hours.
Sources
No outside data or rates: this is plain arithmetic.
6 automated tests check its answers on every change.
About the time duration calculator
Time does not add like ordinary numbers, because it counts in 60s rather than 10s. Add 2:45 and 1:30 on a normal calculator and you get 4.75, which is wrong. The right answer is 4 hours 15 minutes. This calculator does the carrying for you.
It is useful for adding up timesheet entries, working out the total length of a playlist or a video edit, subtracting a lap time from a finish time, or checking how much time is left on a task.
You don’t have to keep minutes under 60. Enter 90 minutes and it will be counted as 1 hour 30 minutes. Decimals work too: 1.5 hours is 1 hour 30 minutes.
The result is shown as hours:minutes:seconds and also as a total in hours, minutes and seconds. Decimal hours are what most payroll and invoicing systems want. If subtracting gives a negative result, it is shown with a minus sign, which means the second duration was longer.
For the time between two clock times, such as a shift from 09:00 to 17:30, use the hours between times calculator.
Questions people ask
How do I add hours and minutes?
Add the minutes, carry every 60 minutes over as an hour, then add the hours. 2:45 + 1:30 = 4:15.
Why can’t I just use a normal calculator?
Because time is counted in base 60. 2.45 + 1.30 = 3.75, but 2 h 45 min + 1 h 30 min is 4 h 15 min.
Can I enter more than 60 minutes?
Yes. 90 minutes is treated as 1 hour 30 minutes.