Time Duration Calculator
Find the time between two moments, or add and subtract durations in h:m:s.
8:30:00 (h:m:s) • 510 min • 30,600 s.
To find the duration between two times, convert each to seconds since midnight and subtract. From 09:15 to 17:45 is 63,900 − 33,300 = 30,600 seconds, which normalizes to 8 h 30 min — the same as 8:30:00 or 510 total minutes.
Two ways to work with time spans
The calculator has two modes. Between two times takes a start and an end time of day and returns the elapsed duration. Add / subtract combines two durations expressed in hours, minutes, and seconds — useful for totalling lap times, stacking video clips, or working out how much study time is left. Every result is shown three ways: as a tidy h:m:s label, as a clock-style h:m:s figure, and as a total in minutes and seconds.
Work entirely in seconds, then split the total back into whole hours, minutes, and seconds.
- 1 Convert each time to seconds since midnight. 09:15 = 9 × 3600 + 15 × 60 = 33,300 s, and 17:45 = 17 × 3600 + 45 × 60 = 63,900 s.
- 2 Subtract the start from the end. 63,900 − 33,300 = 30,600 seconds of elapsed time.
- 3 Handle times that cross midnight. If the end is earlier than the start, add 86,400 s (one day) so an overnight shift like 22:00 → 06:00 reads as 8 h, not −16 h.
- 4 Normalize back to h:m:s. 30,600 ÷ 3600 = 8 h with 1,800 s left; 1,800 ÷ 60 = 30 min, 0 s — so 8 h 30 min, or 510 total minutes.
Carry and conversion rules
Minutes and seconds roll over at 60; the tool normalizes any oversized field for you.
| Amount | Normalizes to | In seconds |
|---|---|---|
| 90 min | 1 h 30 min | 5,400 s |
| 150 s | 2 min 30 s | 150 s |
| 1 h | 60 min | 3,600 s |
| 1 min | 60 s | 60 s |
| 8 h 30 min | 510 min | 30,600 s |
| 24 h | 1,440 min | 86,400 s |
Crossing midnight, negative results, and carries
Overnight spans. When the end time is earlier than the start, the tool assumes the end falls on the next day and adds 24 hours. That makes an overnight shift from 22:00 to 06:00 read as 8 hours rather than a negative span. If you genuinely want a same-day backward difference, swap the two times.
Negative durations. In Add / subtract mode, subtracting a larger duration from a smaller one gives a negative result, shown with a leading minus sign (for example, 45 min − 1 h = −15 min). This is handy for checking whether you are over or under a time budget.
Carries. You do not have to keep minutes and seconds under 60. Enter 90 minutes and the tool reports 1 h 30 min; enter 150 seconds and it reports 2 min 30 s. Everything is summed in seconds first, then split back into whole hours, minutes, and seconds.