Time Duration Calculator
How long did it take, and what time will it be? Enter a start and an end time to get the duration in hours, minutes and seconds and in decimal hours, with dates when the span covers several days. Or switch modes to add or subtract a duration from a time and see whether the result falls on another day.
- Runs in your browser
- No sign-up
- Free to use
Without dates, an end time earlier than the start is taken as the next day.
How to use Time Duration Calculator
- Choose “Time between two times” or “Add or subtract time”.
- Enter the start and end times, with dates if more than a day is involved.
- Or enter a time and the hours, minutes and seconds to add or subtract.
- Read the duration or the resulting time.
Time Duration Calculator features
Seconds precision
Times to the second.
Overnight spans
An end time before the start counts as the next day.
Multi-day spans
Optional dates for durations over several days.
Add and subtract
Shift a time by any duration and see the day change.
Several formats
h:mm:ss, decimal hours, minutes and seconds.
Quick to copy
Copy the result with one click.
When to use Time Duration Calculator
- Timing a task, a journey or a workout.
- Working out the length of a shift or a meeting.
- Finding when something finishes if it starts now and takes 2 h 45 min.
- Converting a duration to decimal hours for billing.
Time Duration Calculator FAQ
How do I calculate the time between two times?
Subtract the start from the end. If the end is earlier on the clock, the span crosses midnight, so add 24 hours: from 22:30 to 01:15 is 2 hours 45 minutes.
What are decimal hours?
Hours written as a decimal number: 2 hours 45 minutes is 2.75 hours. They are used for billing and payroll.
What if the duration is longer than a day?
Enter the start and end dates as well; the calculator includes the days between them.
Does it handle time zones?
No. Both times are taken in the same time zone. The Time Zone Converter on this site converts between zones.
What about daylight saving?
Durations are calculated from clock times. On the night clocks change, the real elapsed time differs by an hour.
Can I add more than 24 hours?
Yes. The result shows how many days later the time falls.
Clock arithmetic
Time arithmetic is awkward because clocks count in sixties and wrap around at midnight. Subtracting 9:45 from 17:15 in your head means borrowing an hour as sixty minutes, and a span that crosses midnight produces a negative result unless you add a day. A calculator makes these steps reliable.
The duration between two times on the same day is simply the end minus the start. When the end is earlier on the clock, the span must cross midnight, so 24 hours are added. When dates are given, the full days between them are included, which allows durations of any length.
Adding a duration to a time is the reverse operation. The result wraps around midnight, and the calculator reports how many days forward or back it lands, which matters for departure times, cooking, medication schedules and anything else that spans the night.
Durations are often needed as decimal hours for timesheets and invoices. Converting minutes to a decimal fraction of an hour, 15 minutes as 0.25 and 20 minutes as 0.333, is a frequent source of billing errors, so the result always includes the decimal form.