Time Difference Calculator

Time arithmetic is awkward because the units are not decimal. Ten past nine to twenty past five is not 8.10 hours, and the mistake is easy to make and costly to repeat every week on a timesheet. This works in minutes throughout and gives you both forms: the hours and minutes people say, and the decimal hours payroll asks for.

Shifts that cross midnight are handled without you having to do anything. An end time earlier than the start is taken as the next morning, so 22:00 to 06:00 is eight hours rather than minus sixteen — the answer a naive subtraction gives and a surprising number of calculators still return.

Breaks can be deducted with one tap, since unpaid breaks are the other thing that makes a timesheet disagree with the clock. The result shows both the gross time and the net, so you can see what was taken off.

The second mode adds or subtracts a duration from a time, and tells you when the answer lands on a different day. That is the part usually left out: a reader that says "04:30" without saying "the next day" has told you half the answer.

Everything is done in whole minutes, deliberately. Floating-point hours introduce rounding errors that accumulate, and timezone-aware date objects would make a shift across a daylight saving change an hour longer or shorter than the clock actually said.