SuCalc
Time, Date & Work

Time Duration Calculator

Updated Aug 24, 2026 Reviewed Aug 24, 2026
Calculate exact elapsed time between two zoned date-times, with seconds, breaks, reversed inputs, and daylight-saving changes.

Exact elapsed time

Enter two date-times

Start date and time

End date and time

Type a city-based IANA identifier such as Europe/London; UTC is also supported.

Optional unpaid or excluded time subtracted after the interval is measured.

Used only when the chosen local time repeats or does not exist.

Daylight-saving transitions are handled explicitly
A local time can repeat when clocks move back or be skipped when clocks move forward. Choose how those rare wall-clock times should resolve.

Result

Calculation summary

Enter values to see the result

Your result, breakdown, assumptions, and warnings will appear here.

Elapsed-time timeline

Instant-to-instant preview

Live preview
Instant-to-instant previewExact elapsed time: 0d 08h 00m 00s. Total decimal hours: 8 h.Exact elapsed time0d 08h 00m 00sTotal decimal hours8 hBreak deducted30 min
The preview resolves both endpoints in the selected zone and updates without replacing the submitted result.

How to use this calculator

  1. 1Enter the start and end date-times.
  2. 2Choose the IANA time zone and DST ambiguity policy.
  3. 3Optionally deduct a break, then calculate exact elapsed time.

Formula

Elapsed seconds = absolute(end instant − start instant) − break seconds

Each wall-clock input is resolved in the selected IANA time zone before the two exact instants are subtracted.

Calculation steps

  • Validate the dates, 24-hour times, time zone, and break.
  • Resolve each local time to an exact instant using the selected DST policy.
  • Order reversed inputs while retaining a warning.
  • Subtract the instants and deduct the break.
  • Decompose the result and show useful totals.

Worked example

09:00 to 17:30 with a 30-minute break equals exactly 8 hours when the UTC offset does not change.

Assumptions

  • Both endpoints use one selected IANA time zone.
  • Elapsed time measures exact instants, not calendar-day labels.
  • The compatible DST policy chooses the earlier repeated time and moves skipped times forward.
  • Break time is deducted after the absolute interval is found.
  • Leap seconds are not separately counted by Unix/POSIX-style timekeeping.

Sources

Frequently asked questions

Does daylight saving time affect the result?

Yes. The inputs become exact instants in the selected zone, so an offset change can make elapsed time differ from wall-clock subtraction.

What is an ambiguous local time?

When clocks move backward, one wall-clock time can occur twice. Choose earlier or later, use compatible, or reject it.

What happens if the end is earlier?

The calculator reports the absolute duration and shows a reversed-input warning.

Can I subtract a lunch break?

Yes. Enter break minutes; the break cannot exceed the interval.

How is this different from the date difference calculator?

This tool measures exact elapsed time with time zones; the date tool compares calendar-only dates.

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