Time Calculator

Add or subtract time values, or sum multiple time entries for a total.

Concrete scenarios: a podcast editor summing six interview segments (12:34 + 8:15 + 14:02 + ...) to check the episode comes in under a 60-minute sponsorship slot; a marathon runner adding split times across 10 km checkpoints to estimate pace; a cook combining "20 min prep + 45 min simmer + 10 min rest" to find when dinner will actually be ready. Each involves moving between minutes, hours, and seconds in ways that basic arithmetic is easy to get wrong when minute-sums spill past 60.

Under the hood, every input is normalized to total seconds, the operation runs in integer arithmetic (so there's no floating-point drift on long sums), and the result is converted back to HH:MM:SS via integer-division and modulo on 3600 and 60. Sums larger than 24 hours display as HH:MM:SS regardless of magnitude — a 72-hour total shows as 72:00:00, not wrapped. The midnight-wrapping behavior only kicks in when you specifically use the Add/Subtract mode with a start-of-day reference, in which case a day indicator surfaces ("next day" or "previous day") so you see the rollover.

Edge cases worth knowing: negative totals in Sum mode (from subtracting a larger value) display as "-HH:MM:SS" rather than rolling back to 24-hour clock time, since the answer is a duration, not a clock time. Compared to a stopwatch app or a spreadsheet [H]:MM:SS format, this tool is quicker for ad-hoc math because you don't need to remember the [H] bracket trick or worry about Excel silently reformatting the cell. Pairs with the Hours Calculator for shift tracking and the Time Duration Calculator for date-and-time spans.