Time Duration Calculator (Add/Subtract Hours, Minutes, Seconds)
Add and subtract time durations like 1:30:00 + 0:45:00 - 0:10:00 across multiple rows, with automatic carrying between seconds, minutes and hours. Handy for timesheet totals and stacking recipe times.
Tips
- Both notations are supported: kanji-style like "1時間30分" and colon-separated like "1:30:00".
- Add as many rows as you need to sum multiple durations. Pick "-" for rows you want to subtract, such as break time.
- A negative total is shown with a leading minus sign, like "-0:15:00", and highlighted in a different color for clarity.
- Click "Load sample" to instantly see a worked example (1h30m + 45m - 10m).
- An entry with 60 or more minutes or seconds is treated as an invalid format and excluded from the total.
Frequently Asked Questions
Side Note — Why time still runs on base 60, not base 10
While most measurements — meters, currency — settled on base 10, time still runs on base 60: 60 seconds to a minute, 60 minutes to an hour. This convention traces back to ancient Babylonian mathematics, where 60 was prized because it divides evenly by 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30, making fraction arithmetic far easier with the tools available at the time.
During the French Revolution, in 1793, France briefly adopted decimal time: 10 hours per day, 100 minutes per hour, 100 seconds per minute. It was logically elegant, but the cost of rebuilding every clock and the mismatch with astronomical calculations meant it never caught on with the public, and it was formally abandoned within a few years, remembered today only as a historical curiosity.
In computing, by contrast, timestamps are almost always converted into decimal "Unix time" (a plain count of seconds) before any arithmetic happens. This tool works the same way internally: every duration you enter is first converted into total seconds, added or subtracted with its sign applied, and only converted back into the familiar base-60 display at the very end, which avoids rounding drift from repeated carrying.