⏱️ Time Duration Calculator

What this tool does

The Time Duration Calculator performs signed-second arithmetic on time durations expressed in any combination of hours, minutes, and seconds. Internally a duration is a single signed totalSeconds number, which means fractional seconds (30.5s), large hour counts (120:00:00), and negative results are all first-class. Six operations:

• Compute — normalize a single duration to days/hours/minutes/seconds plus HH:MM:SS, 1h 30m 45s, and ISO 8601 PT1H30M45S string variants.
• Add — sum 2-100 durations. Useful for stacking job-step timings, video clip lengths, or workout sets.
• Subtract — compute a - b. Negative results are allowed and reflected in the negative: true flag plus signed totals.
• Multiply — multiply a duration by a finite numeric factor (whole or fractional, positive or negative).
• Divide — divide a duration by a non-zero numeric divisor. Zero divisors throw a validation error.
• Between two clock times — compute end − start for two wall-clock times. If crosses midnight is checked and end is at or before start, 24 hours is added to end before subtracting.

Common use cases

• Audio & video editing — sum the runtimes of multiple clips to plan an export bucket, or compute the gap between two timecodes.
• Payroll & timesheets — derive an 8-hour shift between clock-in (e.g. 09:00) and clock-out (e.g. 17:30) including overnight shifts via the crosses midnight flag.
• Athletic timing — break a 02:15:34.5 marathon split into total minutes (135.575) or compute average pace by dividing by the kilometer count.
• Project estimation — multiply a per-unit duration (e.g. 12 minutes per support ticket) by an expected ticket count, or divide a sprint budget across team members.
• API consumers — convert any input form (HH:MM:SS, "1h 30m 45s", total seconds) into the canonical ISO 8601 PT… string for downstream serialization.

Worked examples

• Compute — { hours: 1, minutes: 30, seconds: 45 } → totalSeconds 5445, HH:MM:SS 01:30:45, ISO 8601 PT1H30M45S, totalMinutes 90.75, totalHours 1.5125.
• Compute (overflow) — { seconds: 90061 } → normalized { days: 1, hours: 1, minutes: 1, seconds: 1 }; HH:MM:SS keeps the "stopwatch" form and reports 25:01:01.
• Add — [{ hours: 1, minutes: 30 }, { minutes: 45 }] → 02:15:00 (2h 15m).
• Subtract — { hours: 2 } − { hours: 1, minutes: 30 } → 00:30:00; reverse the operands and the result becomes -01:30:00 with negative: true.
• Multiply — { minutes: 15 } × 4 → 01:00:00; multiply by 2.5 instead and you get 00:37:30.
• Divide — { hours: 1 } ÷ 4 → 00:15:00; dividing by 0 throws Divisor must not be zero.
• Between — start 09:00, end 17:30 → 08:30:00. Set start to 22:00, end to 06:00 with crosses midnight on and you get 08:00:00; leave it off and the result is -16:00:00.

Notes & conventions

• Hours can exceed 24 in the HH:MM:SS field — we never truncate to a day boundary, so a duration of 5 days renders as 120:00:00. Day-aware output is in the normalized.days field.
• Fractional seconds are preserved through every operation. compute({ seconds: 30.5 }) round-trips byte-for-byte.
• Negative components are allowed because a duration is just a signed number of seconds. compute({ hours: -1, minutes: 30 }) evaluates to -00:30:00 (a duration of negative 30 minutes), the same as compute({ seconds: -1800 }).
• Clock times in between() are validated strictly: hour 0-23, minute 0-59, second 0 to less than 60. Calling between with hour 24 throws a validation error.
• NaN and Infinity are rejected. Any component that isn't a finite number throws before any arithmetic happens.