Adding time is base 60, and that is the whole difficulty
Minutes and seconds carry at 60, not at 100, so 2:45 plus 1:30 is 4:15 rather than 3:75. The calculator does the carrying for you and shows the result in three forms at once: clock time, total minutes, and decimal hours.
Decimal hours is the form payroll and invoicing systems want. 4 hours 15 minutes is 4.25 decimal hours; 4 hours 20 minutes is 4.333…, which rounds to 4.33 and is the single most common source of a small, persistent discrepancy on a timesheet. The tool shows the unrounded value so you can see where the difference comes from.
Spans that cross midnight
A shift from 22:00 to 06:00 is eight hours, not minus sixteen. When the end time is earlier than the start time the calculator assumes the span crosses midnight and adds a day. If you genuinely mean a negative span, use subtraction mode.
Worked example — a split shift
06:45 to 11:30 is 4 hours 45 minutes. 13:15 to 18:00 is 4 hours 45 minutes. Together that is 9 hours 30 minutes, or 9.5 decimal hours, or 570 minutes. At an hourly rate this is the number that goes on the invoice; at 9.5 it is exact, which is not always true — see the rounding note above.
Worked example — a flight with a clock change
A flight leaving at 23:40 and landing at 07:20 the next morning is 7 hours 40 minutes of elapsed time if both clocks are in the same zone. If they are not, the wall-clock difference and the elapsed time are different numbers, and only one of them is the flight time. Convert both ends to a single zone first with the time zone converter, then subtract.
Daylight saving is the exception to "a day is 24 hours"
On the day clocks go forward, a day contains 23 hours; on the day they go back, 25. A span crossing one of those transitions has an elapsed time that differs from the wall-clock difference by an hour. Calendar-day arithmetic is unaffected — see the date calculator — but hour arithmetic is not, and this is where naive tools are quietly wrong twice a year.
The convention this calculator uses
Three choices decide every answer on this page, and they are the three that tools quietly make differently. Stated once, here:
- Nothing is rounded until the end. Every span is held in whole seconds and summed exactly. The decimal figure is derived from that total and rounded once, at the point it is displayed. Rounding each span first and then adding gives a different number, and over a month of timesheet rows the difference is real.
- An end time earlier than the start time means the span crossed midnight. 22:00 to 06:00 is eight hours, not minus sixteen. That is the right assumption for a shift and it is wrong roughly never; when you genuinely want a negative result, use subtraction mode, which does not apply the assumption.
- Clock arithmetic, not zone arithmetic. The calculator adds and subtracts wall-clock values. It does not know where you are and does not apply a daylight-saving offset. For a span that crosses a clock change, see the section below.
Minutes to decimal hours, in full
The conversion payroll and invoicing systems want. Divide minutes by 60; the awkward ones are the thirds.
5 min = 0.083 · 6 = 0.1 · 10 = 0.167 · 12 = 0.2 · 15 = 0.25 · 18 = 0.3 · 20 = 0.333 · 24 = 0.4 · 25 = 0.417 · 30 = 0.5 · 35 = 0.583 · 36 = 0.6 · 40 = 0.667 · 42 = 0.7 · 45 = 0.75 · 48 = 0.8 · 50 = 0.833 · 54 = 0.9 · 55 = 0.917.
Only 6, 12, 18, 24, 30, 36, 42, 48 and 54 minutes convert to an exact two-decimal figure. Everything else is an approximation the moment you write it down, which is why a week of 8:20 days does not total to a round number however you round it.
Worked example — five spans that do not agree with their rounded selves
Five days of 8 hours 20 minutes each. Exactly, that is 41 hours 40 minutes, or 41.667 decimal hours. Round each day to 8.33 first and the week totals 41.65 — a minute short of the true figure. Round each day up to 8.34 and it totals 41.70, two minutes long. At $30 an hour, rounding down each day costs 50 cents a week and about $26 a year, per person. This calculator sums the exact values and rounds once, so the figure it gives is 41.67.
Worked example — subtracting to find a start time
A process takes 3 hours 50 minutes and has to finish by 14:15. Subtracting gives a start of 10:25. Subtract another 25 minutes of setup and you get 10:00. Running the subtraction the other way — 14:15 minus 10:25 — returns 3 hours 50 minutes, which is the check worth doing: base-60 subtraction with a borrow is where mental arithmetic fails, because the borrow is 60 and the hand expects 100.
Where other tools give a different answer
- Rounding policy. Tools that round every intermediate value to two decimals drift by a minute or two over a week. We round once.
- Seconds. Some calculators silently truncate seconds to zero. Ours carries them, which is why a total can end in an odd number of seconds rather than a tidy one.
- The midnight assumption. Tools that do not make it return a negative span for an overnight shift; tools that always make it cannot express a negative span at all. We make it in duration mode and not in subtraction mode.
- Daylight saving. A tool built on timestamps rather than clock values will make a span across a US spring-forward Sunday come out an hour shorter than the clocks say. That is arguably the more useful number, but it is a different one, and a tool that does not say which it gives is not usable for payroll.
When you want a date rather than a time
This page does hours and minutes. For arithmetic on calendar days — a deadline, a notice period, an invoice term — use the date calculator, which works on calendar components and is therefore immune to clock changes. For hours worked across a week with breaks deducted, the hours calculator is the one built for timesheets. For a single span between two clock times, the time duration calculator is narrower and quicker. Every convention on this site is written out on the methodology page.