Time Calculator
Add or subtract two durations in hours, minutes and seconds.
Enter durations
Result
Adding and subtracting time correctly
Time arithmetic trips people up because it isn't base-10 — 60 seconds make a minute and 60 minutes make an hour, so you can't add durations the way you'd add plain decimal numbers. This calculator sidesteps that entirely by converting both durations into total seconds first, performing the addition or subtraction on those plain numbers, then converting the result back into hours, minutes, and seconds for display.
That conversion step is what handles "carrying" correctly: if you add 45 minutes to 40 minutes, the calculator doesn't show "85 minutes" — it converts to seconds, adds, and converts back, correctly showing 1 hour 25 minutes. The same logic applies to subtraction; if the second duration is larger than the first, the result is negative, and the calculator displays a minus sign in front of the hh:mm:ss output rather than showing a nonsensical time.
This tool is meant for pure duration math — adding up chunks of elapsed time, like combining several workout segments, tallying video or audio clip lengths, or figuring out total practice time across sessions. If you instead need to know the number of hours worked between a start and end clock time (like 9:00 AM to 5:30 PM), the dedicated Hours Calculator on this site handles that clock-time scenario more directly, including break deductions.
Frequently asked questions
Why doesn't 1:30 + 0:45 equal 1:75? Time carries in base 60, not base 100 — 75 minutes is 1 hour and 15 minutes, so the calculator rolls extra minutes into hours and extra seconds into minutes automatically, the same way a clock would.
Can I subtract a longer duration from a shorter one? Yes — the result will show as negative, which is useful for checking whether a task actually fit inside a time budget.
What format should I use to enter durations? Hours, minutes, and seconds as separate numbers — you don't need to type colons or worry about leading zeros, the calculator handles the formatting for you.
Worked example
Adding 2 hours 45 minutes to a start time of 11:30 AM gives 2:15 PM — the calculator carries the extra 45 minutes past the hour mark and rolls it into the PM period automatically.
Does it handle time zones? No — it calculates elapsed or resulting time within a single time zone; for cross-time-zone math, convert both times to the same zone first.
Can I subtract time instead of adding it? Yes — subtracting works the same way, and the calculator correctly borrows from the hour (or day) when subtracting minutes that would otherwise go negative.