Duration, not clock arithmetic
The gap between 09:15 and 17:45 is 8 hours 30 minutes. Written as a decimal that is 8.5 hours; in total minutes it is 510. All three are shown, because the form you need depends on whether you are filling in a timesheet, an invoice or a form that wants minutes.
Spans longer than a day
Add dates as well as times and the duration can run to days. From 14:20 on 3 May to 09:05 on 6 May is 2 days, 18 hours and 45 minutes, or 66 hours 45 minutes, or 4,005 minutes.
Crossing midnight
With no dates given, a finish time earlier than the start time is assumed to be the next day, so 22:40 to 06:15 gives 7 hours 35 minutes. That is the right assumption for shifts and almost always what is meant. If it is not, supply both dates.
Elapsed time and wall-clock time are not always the same
On the two days a year when clocks change, a span can have a wall-clock difference and an elapsed time that differ by an hour. From 23:00 on the Saturday to 07:00 on the Sunday of the spring change, the clocks say eight hours have passed but only seven have. Which one you want depends on the question — a paid shift is usually elapsed time, a scheduled appointment is usually wall clock. The calculator gives wall-clock arithmetic and flags when a span crosses a transition.
Worked example — a service-level window
A ticket opened at 16:40 on Friday 11 December 2026 with a next-business-day response target is due by the end of Monday 14 December. That is 79 hours 20 minutes of elapsed time but only about 8 working hours, because the weekend is not counted. Service targets quoted in hours almost always mean business hours; check which before you count.
The convention, stated plainly
- With no dates, a finish earlier than the start is the next day. 22:40 to 06:15 is 7 hours 35 minutes. This is the right assumption for a shift and it is the one every timesheet expects; supply both dates when it is not what you mean.
- Wall-clock arithmetic. The duration is the difference between the two clock readings. On the two days a year when clocks change, that is not the same as elapsed time — see below.
- Seconds are carried, not truncated. A total can end in an odd number of seconds. The decimal figure is derived from the exact total and rounded once.
- Nothing is rounded to a quarter hour. If your employer or client rounds, apply that rule to the exact figure rather than the other way round.
The clock-change dates, with the numbers
US clocks go forward on Sunday 8 March 2026 and back on Sunday 1 November 2026; in 2027 the dates are 14 March and 7 November. The EU moves on different dates again — 29 March and 25 October 2026 — which is why a London-to-New-York time difference is five hours for most of the year and four or six for about three weeks of it. A span from 23:00 to 07:00 across the spring change shows eight hours on the clock and seven were elapsed; across the autumn change it shows eight and nine were elapsed. This page gives the wall-clock figure and flags the transition, because which of the two you want depends on the question — a paid shift is usually elapsed time and a scheduled appointment is usually wall clock, and a tool that silently picks one is unusable for the other.
Worked example — a multi-day production window
A run starting at 06:45 on Monday 5 October 2026 and finishing at 22:10 on Thursday 8 October 2026 is 3 days, 15 hours and 25 minutes. That is 87 hours 25 minutes, or 5,245 minutes, or 87.417 decimal hours. Notice that the day figure and the hour figure are not independent: 3 days and 15 hours is only 87 hours because none of those days crossed a clock change. Move the same window to the first week of November, when US clocks go back, and the elapsed total becomes 88 hours while the calendar description stays identical.
Where other duration calculators disagree
- The overnight assumption. Tools that do not make it return a negative duration; tools that always make it cannot express one.
- Elapsed versus wall clock. A tool built on timestamps gives elapsed time and will differ from this page by an hour on two days a year.
- Decimal precision. Two decimal places loses up to eighteen seconds. Fine for one span, visible across a hundred.
- Business hours. Some service-level calculators count only working hours. That is a different measure entirely, and the difference is large: the example below is 79 hours of elapsed time and about 8 working hours.
Related tools
For a week of shifts with breaks deducted and a weekly total, the hours calculator is the right page. For adding several durations together rather than measuring one, use the time calculator. For spans measured in calendar days rather than hours, use days between dates, which is immune to clock changes because it works on calendar components. If your times are recorded in 24-hour form, the military time converter has the full chart.