Time Duration Calculator

Adding and subtracting times without slipping

Time arithmetic trips people because it is base 60 for minutes and seconds but base 24 for hours, so ordinary decimal intuition fails. Ninety minutes is 1.5 hours as a decimal but 1:30 in clock notation, and mixing the two is the single most common error — adding 1.30 and 1.45 as decimals gives 2.75, while adding 1:30 and 1:45 as times gives 3:15. They are not the same quantity.

The reliable method is to convert everything to a single small unit, do the arithmetic, then convert back. Total the minutes, then divide by 60 for hours and take the remainder as minutes. Two further cases need care: a span crossing midnight needs 24 hours added to the end time before subtracting, or you get a negative result; and payroll conventions often round to the nearest quarter-hour, so a calculated duration and a paid duration can legitimately differ. Where a span crosses a daylight-saving change, the elapsed clock time and the true elapsed time differ by an hour.

Worked example

A night shift runs from 22:00 to 06:30. Because the end time is on the next day, add 24 hours to it: 06:30 becomes 30:30. Then subtract: 30:30 − 22:00 = 8 hours 30 minutes. As a decimal for payroll, that is 8.5 hours.

Converting minutes to decimals catches people out. 7 hours 45 minutes is 7.75 hours (45 ÷ 60 = 0.75), not 7.45. Paying 7.45 hours instead of 7.75 underpays every such shift by 18 minutes.

Common mistakes to avoid

• Writing minutes as decimal digits, such as 7:45 as 7.45 hours.
• Forgetting unpaid breaks. An 8:30 shift with a 30-minute unpaid break is 8 paid hours.
• Ignoring daylight saving changes for overnight shifts in countries that use it. India does not, but the UK, US and Europe do.

Last reviewed: 5 November 2026 by the YogiCalc team · How we calculate and verify · Spotted an error? Tell us