Why time will not add up like normal numbers
Time is base 60, so ordinary decimal arithmetic goes wrong the moment minutes are involved: 1:45 plus 1:30 is not 2.75 plus nothing sensible, and typing 1.45 into a normal calculator makes it worse. The reliable method, and the one this tool uses, is to convert both durations to minutes, add or subtract, then convert back. There is no rounding at any point, so the h:mm answer is always exact. The decimal hours figure is provided alongside because timesheets and payroll systems want it, and converting between the two by eye is where most mistakes happen. Working in minutes also avoids the classic pen-and-paper slip of borrowing ten instead of sixty when a subtraction crosses an hour boundary.
Worked examples
h:mm or decimal hours?
Both formats describe the same duration, but they are read differently and mixing them up costs real money on a timesheet. In h:mm the part after the colon is minutes out of 60, so 7:30 means seven and a half hours. In decimal hours the part after the point is a fraction of an hour, so seven and a half hours is 7.5, and 7.30 would actually mean 7 hours 18 minutes. The rule of thumb: colons mean minutes, points mean fractions. When you need to convert, divide the minutes by 60 (30 ÷ 60 = 0.5) or, going the other way, multiply the fraction by 60. A quick sanity check: 45 minutes should show as 0.75 of an hour, so if a figure ends in .45 someone has probably typed minutes where a fraction belongs.
Everyday uses
- Timesheets: add the week's shifts together in h:mm, then submit the decimal total.
- Overtime: subtract your contracted hours from the hours you actually worked.
- Journeys: add legs of a trip, or subtract a delay from a planned duration.
- Editing and cooking: combine clip lengths or oven stages that are given in minutes.
- Study and exercise: total up sessions logged as odd scraps of hours and minutes.
- Payroll checks: confirm the decimal total on a payslip matches the h:mm hours you recorded.
For the common first step, working out a single shift from its start and end times, use the hours calculator, then bring the results here to build a weekly total. Minutes over 59 are welcome: 90 minutes is simply treated as an hour and a half, so you can type durations exactly as a recipe or a running app gives them. Everything runs in your browser, and nothing you type is uploaded anywhere.
Frequently asked questions
How do I add more than two durations?
Chain the results. Add the first two durations, then use the total as the first duration and add the next one, and so on. Because the tool works in whole minutes there is no rounding error when you chain, unlike adding decimal hours.
What happens if I enter 90 minutes?
Minutes over 59 are perfectly fine. The calculator converts everything to minutes before doing the sum, so 1 hour 90 minutes is treated as 2 hours 30 minutes and the result is shown normalised.
Can the result be negative?
Yes. If you subtract a longer duration from a shorter one the result is shown with a minus sign, for example -1:30. That is useful for working out how far behind a target you are.
How do I turn decimal hours back into hours and minutes?
Keep the whole hours, then multiply the decimal part by 60. So 3.58 hours is 3 hours plus 0.58 times 60, which is about 35 minutes. This tool shows both formats so you rarely need to do it by hand.
Why do timesheets use decimal hours?
Pay is hours multiplied by an hourly rate, and that multiplication needs a decimal. 7:30 must be entered as 7.5, because typing 7.30 would count only 18 minutes past the hour and underpay you by 12 minutes.