Time Duration Calculator

Time between two times

Add or subtract time

How time durations are calculated

Both tools work in plain elapsed seconds, then convert back into the units people think in:

Total seconds = end time − start time, split as: days = total ÷ 86,400; hours = remainder ÷ 3,600; minutes = remainder ÷ 60; seconds = the rest.

Adding a duration = start time + (hours × 3,600 + minutes × 60 + seconds), rolling over midnight, month ends, and leap years automatically — the date math is handled by the calendar, not by counting 30-day months.

Overnight and ordering: the duration tool always reports a positive span — if the end time is earlier than the start, the two are treated in reverse order (so 5 PM to 9 AM the next morning works as long as the second date is the next day; enter the next day's date, not just the clock time). Times are read in your device's local time zone, and a span crossing a daylight-saving change reflects real elapsed clock time.

Common uses: work shifts and timesheets, elapsed time for experiments and cooking, medication intervals, travel legs with layovers, and "what time do I need to leave" planning with the add/subtract tool.

Frequently asked questions

Why not just subtract the clock times? Clock subtraction breaks across noon, midnight, and month boundaries (17:00 minus 09:00 is fine; 02:00 minus 22:00 is not). Converting both times to a single elapsed-seconds count first is what makes the answer reliable.

Does this count business hours? No — this is total elapsed time, weekends and holidays included. For working days between dates, use the business days calculator on this site.

Can I add more than 24 hours? Yes — the hours field accepts any number, so adding 100 hours rolls forward just over four days, with the resulting date shown in the result.