Calculators & everyday math
Calculating Overnight Time Spans
A night shift from 10:00 PM to 6:00 AM, a late event, a trip that ends after midnight: when a span crosses midnight, plain subtraction gives a negative number. This guide shows the fix and the cases where clock times alone can’t give the right answer.
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Add 24 hours to the end time
If the end time is earlier than the start time, the end is on the next day. Add 24 hours to it before subtracting: 10:00 PM to 6:00 AM becomes 30:00 − 22:00 = 8 hours.
Examples
| Start | End | Time between |
|---|---|---|
| 10:00 PM | 6:00 AM | 8 hours |
| 11:30 PM | 7:15 AM | 7 hours 45 minutes |
| 6:45 PM | 1:10 AM | 6 hours 25 minutes |
| 11:59 PM | 12:00 AM | 1 minute |
Spans of 24 hours or more
Clock times repeat every day, so they can’t show how many days passed: 9:00 AM to 9:00 AM could be 0 hours or 24, and 8:00 AM to 10:00 AM could be 2 hours or 26. For longer spans, add the time as durations with the Time Duration Calculator.
Nights when the clocks change
Where daylight saving time is used, clocks jump forward an hour one night a year and back an hour another night. On the spring night, a shift from 10:00 PM to 6:00 AM lasts 7 hours of real time; on the autumn night, 9 hours. A clock-time calculator shows 8 hours both times, so adjust by hand on those nights.
Overnight Time Spans FAQ
- How do I calculate hours for a night shift?
- Add 24 hours to the end time, then subtract the start time: 10:00 PM to 6:00 AM is 8 hours.
- Why do I get a negative number?
- The end time is on the next day. Add 24 hours to it first.
- What about spans longer than 24 hours?
- Clock times can’t show them. Add the time as durations instead.
- Does daylight saving time affect overnight shifts?
- On the two nights the clocks change, the real elapsed time is an hour shorter or longer than the clock difference.
- Is midnight the start or the end of a day?
- 12:00 AM (00:00) is the start of a day, so a span ending at midnight ends at the start of the next day.
Related guides
Open the tool
Jump into Hours Between Times Calculator when you are ready to process your files.
