Duration calculator
Add or subtract times like 01:30:00 and 00:45:00, or convert a value such as 2 hours into seconds and hours.
- Runs in your browser
- No upload
- Instant result
Assumptions & formula
Formula and assumptions
Σt; t₁−Σ(t₂…tₙ); 1d=24h=1440min=86400s
HH:MM:SS.sss sums and differences use exact integer milliseconds. Unit conversions round the formatted duration to the nearest millisecond, with halfway values away from zero. Decimal seconds and hours are approximate displays.
Results
Enter values and press Calculate to see the result here.
How to use this calculator
- Set inputs and units
Choose add, subtract or unit conversion, and enter one elapsed duration per line as hours:minutes:seconds.
- Calculate
Check this worked example: 01:30:00 +00:45:00 → 2:15:00.000 =8100 s
- Results
Subtraction takes the later lines away from the first. The result may be negative, and hours may exceed 24.
Questions and limits
Does one day always mean 24 hours here?
Yes. This is elapsed-duration arithmetic. A civil day around a daylight-saving change is a different timezone calculation.
Which input errors should I correct?
Keep minutes and seconds within their clock fields. Use at most 1,000 lines and valid decimal numbers for conversions.
What does this calculation leave out?
The final duration is rounded to milliseconds. There are no dates, payroll rules, timezone transitions or working-hour policies.