Duration calculator
Add or subtract precise durations and see the result in hours, days and milliseconds.
How it works & useful details
How it works & limits
Enter H:MM:SS, optionally with a sign and up to three fractional second digits, such as -1:30:00.250. Hours may exceed 24 and can contain up to nine digits. Minutes and seconds must be 00–59.
Arithmetic is exact in milliseconds. A day is always 24 hours. These are fixed durations: calendar months and timezone/DST changes are not involved. A negative result applies to the entire breakdown.
Your working space
Explore the live preview, then save a copyable text report. Inputs stay on this device and are cleared by refreshing. Dates use the Gregorian calendar, including before its historical introduction.
About this tool
Duration calculator adds or subtracts precise lengths of time and shows the result in several units, from minutes to days. It is useful for combining task times, offsetting timestamps, or converting a duration into a different unit.
Because durations are treated as exact amounts rather than calendar dates, the math does not depend on month lengths or daylight saving changes. All conversions run locally.
How to use it
- Enter the duration components, such as hours, minutes, and seconds.
- Choose whether to add or subtract them.
- Optionally enter a base duration to adjust.
- Read the result in each unit and copy the value you need.
Worked example
Adding 1:45:30 and 0:30:45 gives 2:16:15, which is 8,175,000 milliseconds. Seconds carry into minutes and minutes into hours, just like adding columns by hand: 30 + 45 seconds is 75, so write 15 and carry 1 minute.
Subtraction can go negative. 0:30:00 − 1:15:00 is −0:45:00, and the sign applies to the whole breakdown.
Typical uses
- Totalling timesheet entries or video clip lengths.
- Finding the gap between two lap or split times.
- Converting a long duration such as 100:00:00 into days and hours (4 days, 4 hours).
- Working with precise media timings that include milliseconds, such as 0:00:03.250.
Durations are fixed lengths: a day is always exactly 24 hours, and months are not involved. That keeps the arithmetic exact, but it also means a duration is not the same as the time between two wall-clock times on either side of a daylight-saving change.
Frequently asked questions
How is a duration different from a date range?
A duration is an exact span of time, while a date range is measured in calendar days. Use the Date difference tool for calendar spans.
Can the result be negative?
Yes. Subtracting more than the starting amount produces a negative duration, which is shown explicitly.
Which units are supported?
Hours, minutes, seconds, and milliseconds, with combined output in larger units such as days.
Can the hours exceed 24?
Yes. Hours can have up to nine digits, so long totals like 250:30:00 are accepted and broken down into days, hours, minutes, and seconds.