Time Duration Calculator - Add, Subtract & Multiply Durations

How to use this tool

Choose an operation. Pick Add, Subtract, Multiply, Divide, or Average.
Enter durations. Type one duration per line in any supported format (1:30:00, 90m, 1h 30m, etc.).
Read the result. The total is shown in HH:MM:SS, seconds, minutes, decimal hours, and 24-hour elapsed days.

Add, Subtract & Combine Durations

This tool works with pure durations (no calendar dates required). It's useful for adding up video clip lengths, calculating total work time from a list of sessions, or figuring out what remains after subtracting elapsed time from a total.

Supported Formats

The parser accepts many common formats so you can paste durations from different sources without reformatting them first. Supported: 1:30:00, 1:30, 1d 2h, 1 day, 1h 30m, 1h30m, 90m, 5400s, 1.5h, or plain numbers (treated as seconds). Negative values are also accepted. A day always means 24 elapsed hours; it does not refer to a calendar day.

Operations

Add sums all durations. Subtract starts from the first duration and subtracts the rest. Multiply multiplies the total by a factor: useful for estimating repeated tasks. Divide splits the total: useful for calculating per-unit time. Average divides the total by the count of items.

Worked examples

Adding video clip durations: four clips of 1:32:10, 0:45:20, 2:10:05, and 0:55:30 - add them to get 5:23:05 of raw footage before editing.
Subtracting a lunch break: total shift 8:30:00 minus break 0:45:00 = 7:45:00 of billable time.
Estimating a repeated task: one task takes 0:08:30 - multiply by 24 to estimate the time for a batch job.

Edge cases

Durations greater than 24 hours: results display as 25:30:00 (not rolling over to the next day), and the elapsed-days total is 1.0625. Durations are elapsed time, not clock readings.
Negative results: subtracting more time than is available produces a negative duration, displayed with a minus prefix.

ISO 8601 duration format

ISO 8601 duration strings are common in APIs, databases, and programming languages. For example, P1DT2H30M represents one day, two hours, and thirty minutes, while PT45S represents 45 seconds.

This calculator does not parse ISO 8601 strings or produce them for copying. Enter the equivalent as 1d 2h 30m instead. Here, d always means 86,400 elapsed seconds; calendar months and years are not supported because their lengths vary.

Frequently asked questions

What formats can I enter?

The parser accepts formats such as 1:30:00, 1:30, 1d 2h, 1 day, 1h 30m, 90m, 5400s, and 1.5h. Mixed formats in the same list are fine. Day units always mean 24 elapsed hours.

How does multiply work?

Multiply takes the sum of all durations and multiplies it by the given factor. For example, if your list sums to 1 hour and you multiply by 2, the result is 2 hours.

Can results be negative?

Yes - subtract operations can produce a negative total. The result is displayed with a leading minus sign, e.g. -0:30:00.

What happens with invalid rows?

Invalid rows are skipped and listed in orange below the duration input. The calculation uses only the valid rows.

How are elapsed days calculated?

One elapsed day is exactly 24 hours (86,400 seconds). This is elapsed-time arithmetic, so it does not account for calendar dates, daylight saving changes, or months and years.