How the duration is measured
Each end of the span combines a date and a time of day into a single moment, expressed as a millisecond timestamp. The calculator subtracts the start moment from the end moment to get the elapsed milliseconds, then converts that into the various units shown.
Because both the date and the time are taken into account, the result is precise to the minute — unlike a plain date difference, this tool can tell you the gap between, say, 9:00 on Monday and 17:30 on Tuesday rather than just "one day".
Totals versus the breakdown
The breakdown gives whole days, hours and minutes — the natural way to describe how long something lasted. The total rows restate the same span entirely in one unit each: total days (with decimals), total hours and total minutes.
Single-unit totals are useful for further math, such as multiplying total hours by a rate or comparing two durations. The breakdown and the totals always describe the same elapsed time.
Tips and caveats
Worth noting:
- The end must be on or after the start; a reversed span returns an error instead of a negative duration.
- Enter times in 24-hour HH:MM format.
- The calculation uses raw elapsed time and does not adjust for daylight-saving changes between the two moments.
- For a pure day count without times, the date or day counter calculators are simpler.
Formula
duration = (endDate+endTime) − (startDate+startTime)