How it is worked out
convert everything to minutes, add or subtract, then divide by 60
Why it is done this way
Hours and minutes cannot be added like decimals, because minutes carry at 60 rather than at 100. The only safe method is to convert every entry to minutes, do the arithmetic there, and convert back at the end.
Step by step
- Convert each entry to minutes: 8:30 is 510
- Add or subtract the minute totals
- Divide the result by 60 for the whole hours
- The remainder is the minutes
What is worth knowing
The decimal figure is the one payroll uses and the hours-and-minutes figure is the one people write down, which is exactly where the mistakes come from: 8:30 is 8.5 decimal hours, not 8.3. Over a week of shifts that confusion costs real money in either direction. This calculator accepts all three notations — 8:30, 8.5 and 510 — because timesheets in practice mix them. If you subtract more than you had, the result is negative and it says so rather than quietly showing an absolute value.