Time duration calculator

How time duration is worked out

Take the end moment, subtract the start moment, and split the result into days, hours and minutes. Across midnight the date moves on by one; across several days, each full day adds 24 hours.

Duration = end date and time − start date and time
Total hours = days × 24 + hours + minutes ÷ 60

Worked examples

Daylight saving time

In the US, federal law sets daylight saving time to start at 2:00 AM on the second Sunday of March and end at 2:00 AM on the first Sunday of November. A state, or the part of a state in one time zone, can keep standard time all year. Other countries change their clocks on other dates; the calculator uses the time zone your device is set to.

• Spring forward: at 2:00 AM the clock jumps to 3:00 AM. A time between 2:00 and 2:59 AM on that night does not exist; if you enter one, the calculator moves it on by an hour and says so.
• Fall back: at 2:00 AM the clock goes back to 1:00 AM and that hour repeats. A time between 1:00 and 1:59 AM that night is ambiguous; the calculator uses the first one.
• No daylight saving in the US: Arizona (the Navajo Indian Reservation there does observe it), Hawaii, Puerto Rico, Guam, the U.S. Virgin Islands and American Samoa. If your device is set to one of these, no change is applied.

When a change falls between your two moments, the result panel also shows the plain clock difference.

15 U.S.C. 260a; NIST, Daylight Saving Time.

Which calculator to use

For two clock times without dates, such as 9 to 5 or 10 PM to 6 AM, the hours calculator is quicker. For a work shift with an unpaid break, use the hours worked calculator.

Questions

Sources

1. 15 U.S.C. 260a, Advancement of time or changeover dates (GovInfo)
2. NIST Time and Frequency Division: Daylight Saving Time

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