Time Duration Calculator
Add two durations or subtract the second from the first. Hours may go past 24.
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How to add durations
- Enter days, hours, minutes, and seconds for duration A.
- Add or subtract B, or convert A into every unit.
- Read clock time, days plus time, and totals in days, hours, minutes, and seconds.
- Hours on the clock may go past 24.
Duration arithmetic
Sum or difference of two time lengths
| Input | Hours, minutes, and seconds for A and B |
|---|---|
| Add | A + B |
| Subtract | A − B |
| Output | Normalized HH:MM:SS and total hours |
Adding and subtracting h:m:s
Each side is hours, minutes, and seconds. Minutes and seconds may be 60 or more; they are normalized (70 minutes is 1 hour and 10 minutes). Add returns the sum. Subtract returns A minus B and may be negative.
Carry and borrow
The result is shown as HH:MM:SS with minutes and seconds in 0–59, plus a decimal hour total. This is clock arithmetic, not a timesheet with unpaid breaks. For calendar dates use date difference.
Not a time zone tool
Crossing a DST change is not the same as subtracting two durations. Convert wall times with the time zone converter, then subtract if you need elapsed clock time in one zone.
Time duration questions
Does this page upload what I type?
No. The work runs in the page you opened. CZNull does not receive the input.
Can minutes be 90?
Yes. 90 minutes is stored as 1 hour 30 minutes before the operation.
Negative results?
Subtract can be negative when B is larger than A.
Is this a stopwatch?
No. You type both sides. It does not read this device's clock.
Days?
Hours may be larger than 24. There is no separate day field on this page.