Time duration calculator
A time duration calculator finds the interval between two dates and times. The result can be shown in days, hours, minutes, seconds or decimal hours. For elapsed time across a clock change, use the correct UTC offset at each endpoint; comparing clock labels alone can produce a different answer.
Multi-day
No guessing a midnight rollover
Two modes
Clock labels, or elapsed with the offsets you supply
Zone-independent
The same inputs give the same answer anywhere
Use the time duration calculator
Enter both endpoints. Clock-time mode compares the labels you typed; elapsed mode uses the UTC offset you give for each endpoint. The calculator never guesses a timezone.
Duration
Enter a start and an end date and time to see the interval.
This interval is out of date. Fix the highlighted field to update it.
- Total duration
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- Hours:minutes:seconds
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- Decimal hours
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- Total minutes
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- Total seconds
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- UTC instants
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Assumptions
No timezone is inferred
In clock-time mode the labels are compared as typed. In elapsed mode you supply the UTC offset at each endpoint; the calculator does not look up an IANA timezone or resolve ambiguous local times. A day means 24 elapsed hours.
Calculated in your browser. Dates, times and offsets are not sent to a server or written to the page address. Consented analytics record only that an interval was calculated and which mode was used.
Time calculator
How duration is calculated
Each endpoint becomes a count of seconds: the date as a day number times 86,400, plus the seconds since midnight. The duration is the end count minus the start count, then split into days of 24 hours, hours, minutes and seconds. Decimal hours are the total seconds divided by 3,600, rounded only for display.
Because the arithmetic uses the labels you typed, the browser's timezone never enters the calculation. Two people in London and New York entering the same values get the same answer.
Elapsed time
Clock time versus elapsed time
UTC offsets
In elapsed mode you give the UTC offset in force at each endpoint, such as +00:00 for GMT, +01:00 for British Summer Time or -05:00 for Eastern Standard Time. Each endpoint is converted to UTC by subtracting its offset, and the interval is the difference between those instants. Offsets run from -12:00 to +14:00 in quarter-hour steps; the display format never changes an instant.
Daylight-saving changes
On 29 March 2026 UK clocks move from 00:30 GMT to 02:30 BST in one elapsed hour. Clock-time mode reports two hours because the labels are two hours apart; elapsed mode with +00:00 and +01:00 reports one. In the autumn the same labels with +01:00 then +00:00 give three. The calculator does not detect these changes for you; it applies the offsets you supply.
Reference
Worked examples
| Start | End | Mode | Duration | Decimal hours |
|---|---|---|---|---|
| 2026-09-22 09:00 | 2026-09-23 10:30 | Clock time | 1 day 1 h 30 m | 25.50 |
| 2026-03-29 00:30 (+00:00) | 2026-03-29 02:30 (+01:00) | Elapsed | 1 h 0 m | 1.00 |
| 2026-03-29 00:30 | 2026-03-29 02:30 | Clock time | 2 h 0 m | 2.00 |
| 2026-10-25 00:30 (+01:00) | 2026-10-25 02:30 (+00:00) | Elapsed | 3 h 0 m | 3.00 |
| 2026-01-01 00:00:15 | 2026-01-03 01:02:03 | Clock time | 2 days 1 h 1 m 48 s | 49.03 |
Related tools
When to use an hours or time-card calculator
This tool measures one interval. If you need to take an unpaid break out of a shift, use the hours calculator. If you need a week or fortnight of daily rows with overtime and a CSV, use the time-card calculator. Both keep the same whole-second arithmetic.
Months and years are deliberately not offered as units: their length depends on which calendar months the interval spans, so a single number would be a calendar interpretation rather than a duration.
Frequently asked questions
Time duration questions
Can I calculate across several days?
Yes. Enter both dates and times. The result shows the full interval rather than assuming that an earlier finish time means the next day.
What is the difference between clock time and elapsed time?
Clock-time mode compares the entered calendar labels without timezone adjustments. Elapsed-time mode uses the UTC offset you supply for each endpoint.
Does the tool automatically detect daylight saving?
No. In v1, you supply the correct offset at each endpoint. It does not infer an IANA timezone or resolve ambiguous local times automatically.
Does one day always mean 24 hours?
The output unit "day" is 24 elapsed hours. A local calendar day around a clock change can have a different elapsed duration, so the selected mode matters.
Can I subtract lunch or calculate pay?
Use the hours calculator for one shift with breaks or the time-card calculator for weekly hours and gross-pay estimates. This tool measures an interval.
What if the end is before the start?
The tool asks you to correct the endpoints. It does not silently swap them or return a misleading positive duration.
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Next step
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