Math & Dates Time calculator
Add or subtract durations, or total a whole list of them, in any format people actually type: 1:30, 90m or 1h 30m.
Durations can be written as 1:30, 1:30:45, 1h 30m, 90m or 1.5h. A bare decimal is read as hours, a bare whole number as minutes.
Result
2:15:00
2h 15m
Decimal hours
2.25
What payroll and invoicing want.
- Hours
- 2
- Minutes
- 15
- Seconds
- 0
- Total minutes
- 135.0
- Total seconds
- 8,100
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Reembun. (2026, July 28). Time calculator. https://reembun.com/time-calculator
How to use it
Choose what to calculate
Add or subtract two durations, or total a whole list of them.
Enter the times
Hours, minutes and seconds per row. The plus and minus buttons set the operation between them.
Read the total
The answer appears in hours, minutes and seconds, with the total in minutes and in seconds alongside for anything that needs a single unit.
Formats it accepts
The main reason a time calculator is frustrating is that most only accept one input format. This one accepts the ones people actually type:
| You type | It reads |
|---|---|
1:30 | 1 hour 30 minutes |
1:30:45 | 1 hour 30 minutes 45 seconds |
:45 | 45 minutes |
1h 30m | 1 hour 30 minutes |
90m | 90 minutes |
2 hours | 2 hours |
1.5h | 1 hour 30 minutes |
1.5 | 1 hour 30 minutes |
90 | 90 minutes |
The last two are the genuinely ambiguous ones. A bare decimal is read as hours and a bare integer as minutes, because that matches how people mean them, and getting it backwards produces answers that are obviously wrong, which is worse than asking.
Decimal hours, and why they matter
Timesheets, invoices and payroll systems want decimal hours. The conversion is division by 60, not moving the decimal point:
| Time | Decimal hours |
|---|---|
| 0:15 | 0.25 |
| 0:30 | 0.50 |
| 0:45 | 0.75 |
| 1:20 | 1.33 |
| 1:45 | 1.75 |
| 7:30 | 7.50 |
Entering 1:45 as “1.45” understates 45 minutes as 27, an 18-minute error per entry, which compounds fast across a timesheet.
Worked examples
Adding two durations. 1:30 + 0:45 = 2:15, or 2.25 decimal hours.
Subtracting. 2:00 − 2:30 = −0:30. You ran half an hour over.
Totalling a list. Four tasks at 1:30, 0:45, 2:15 and 0:20 total 4:50, or 4.83 decimal hours, with an average of 1:12.
Where duration arithmetic goes wrong
Treating 1.5 hours as 1:50. The decimal and the clock use different bases: 1.5 hours is 1:30. Mixing the two is the most frequent error in manual time tracking.
Adding minutes past 60. 45 + 45 is 90 minutes, which is 1:30, not 1.30 and not 0:90. Carrying at 60 rather than 100 is the whole difficulty.
Rounding at each entry. Rounding every task to the nearest quarter hour and then summing accumulates bias. Sum the exact durations and round once at the end.
Working in seconds internally
All arithmetic here happens in whole seconds, which means repeated addition and subtraction cannot accumulate floating-point drift. Adding a hundred durations of 0:00:01 gives exactly 0:01:40, not something ending in a trail of nines, a small guarantee that matters when a total is being invoiced.
Common questions
What formats can I type?
Colon form like 1:30 or 1:30:45, unit form like 1h 30m or 90m, and decimals like 1.5h. A bare decimal is read as hours and a bare whole number as minutes, because that is how people mean them. 1.5 almost always means an hour and a half, and 90 almost always means ninety minutes.
Why do I need decimal hours?
Payroll, invoicing and timesheet systems almost universally want decimal hours rather than hours and minutes. 1:45 is 1.75 hours, not 1.45, and entering the latter is a common and expensive mistake, because it understates 45 minutes as 27.
Can the result be negative?
Yes. Subtracting a longer duration from a shorter one gives a negative result, shown with a leading minus. That is usually what you want when calculating how far over or under an estimate you ran.
How is this different from the date calculator?
This works with durations, meaning spans of time with no position on the calendar. The date calculator works with dates. Adding 90 minutes to 45 minutes is a duration question; working out how many days until March is a date question.
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