Time Duration Calculator
Measure the exact duration between two moments — down to the second. Use two clock times for same-day (or overnight) spans, or switch to date mode for durations that cross days, months, or leap years, with the answer shown in every unit at once.
Clock mode assumes the next day when the end time is earlier than the start time. Seconds are optional — leave them at :00 if you don’t need them.
How duration between two times is measured
Both moments are converted to seconds on a single timeline and subtracted — the classic borrow-the-60 subtraction you’d do by hand, done exactly. The result is shown as a combined duration (days, hours, minutes, seconds) and as a total in each unit, because a payroll system may want 8.5417 hours while a lab log wants 30,750 seconds. Date mode runs the same subtraction across calendar days, so a span over February 29 in a leap year comes out one day longer, automatically.
How it’s calculated
Duration = end timestamp − start timestamp, computed with UTC calendar math (immune to daylight-saving clock jumps). Combined form: days = ⌊s ÷ 86,400⌋, then hours, minutes, seconds from the remainder. Totals: hours = s ÷ 3,600; minutes = s ÷ 60.
Results update as you type. Durations are exact calendar time — if your use case follows local DST wall clocks, a spring-forward night is 1 real hour shorter than the clock suggests.
Worked example
From 9:15:00 AM to 5:47:30 PM the duration is 8h 32m 30s — 0.3559 days, 8.5417 hours, 512.5 minutes, or 30,750 seconds. In date mode, Feb 27, 2026 10:00 PM to Mar 1, 2026 6:30 AM is 1 day 8h 30m (32.5 hours); the same dates in leap-year 2024 span 2 days 8h 30m (56.5 hours) because of February 29.
Common mistakes
- Subtracting clock times by hand without borrowing 60 for the minutes (13:57 − 9:58 is 3:59, not 4:01).
- Forgetting the extra day when a range crosses February 29 in a leap year.
- Reading 8.5417 hours as 8 h 54 m — the decimal part is fractions of an hour, not minutes.
- Using clock mode for spans longer than 24 hours — switch to date mode.
Where it is used
- Timing experiments, renders, backups, or batch jobs to the second.
- Logging flight, race, or process durations that cross midnight.
- Converting a duration into seconds or minutes for spreadsheets and scripts.
- Working out precise elapsed time between two timestamped events.
Frequently asked questions
What if the end time is before the start time?
In clock mode the calculator assumes the span crosses midnight and adds 24 hours, so 10:30 PM to 1:15 AM returns 2h 45m. In date mode, an end before the start is flagged instead — swap your dates.
Does it count seconds?
Yes. Both time pickers accept hours, minutes, and seconds, and the duration is computed and displayed to the second. Leave seconds at :00 if you only care about minutes.
How are leap years handled?
Exactly. Date mode counts real calendar days, so Feb 27 10:00 PM to Mar 1 6:30 AM is 32.5 hours in 2026 but 56.5 hours in 2024, which has a February 29.
Does daylight saving time change the result?
No — the math uses a fixed 24-hour day. If you specifically want wall-clock elapsed time across a DST change in your time zone, add or subtract the one shifted hour yourself.
How do I convert a duration to decimal hours?
Divide total seconds by 3,600 — the “In hours” line does it for you. 8h 32m 30s is 30,750 s ÷ 3,600 = 8.5417 hours.