Free · Everyday calculations

Time Span in Hours, Minutes & Seconds

Subtract two times on the same timeline or solve for a start or end time.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Edit a calculated value to solve backwards, or lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

From 09:15:00 to 17:45:00 is 8.5 hours, or 8 hours 30 minutes. The end time must be at or after the start time.

Duration = end time − start time

Worked example

Enter these known values and leave the other values blank.

Start time / elapsed offset
9:15:0 hrs / min / sec
End time / elapsed offset
17:45:0 hrs / min / sec
Duration
8.5 hrs

Assumptions and limitations

  • Enter colon-separated hours:minutes:seconds in the compound fields. Both offsets must share one origin; the calculator does not infer dates or automatically wrap an earlier clock time to tomorrow.
  • For a span crossing midnight, include the extra day in the end offset: 23:30:00 to 25:00:00 is 1.5 hours. Time zones, daylight-saving changes, leap seconds and unpaid breaks are outside this model.

Common questions

How do I enter a shift that ends after midnight?

Express the end as hours from the same starting midnight. For example, 01:00 on the following day is 25:00:00. Entering 01:00:00 after 23:30:00 would put the end before the start and is invalid.

Can I find an end time from a duration?

Yes. Leave the end field blank, then enter the start offset and the duration in the displayed units. The result is an elapsed offset; convert offsets over 24 hours to a date and clock time if needed.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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