A time calculator adds and subtracts hours and minutes, which ordinary arithmetic gets wrong because time runs in sixties rather than tens. Add and subtract hours, minutes, and seconds without the base-60 headache - and convert decimal hours (7.75 = 7h 45m) for timesheets, both directions.
Time doesn't carry in tens - it carries in sixties. 2:45 plus 1:30 isn't 3:75, it's 4:15, because 75 minutes rolls over into an extra hour. This tool does all its arithmetic in seconds underneath (so the carrying is always exact), then converts back to hours, minutes, and seconds at the end - and shows the total in every unit so you can sanity-check it.
Payroll systems and invoices often use decimal hours - 7.75 hours means 7 hours and 45 minutes, because 0.75 of an hour is 45 minutes, not 75. Reading the decimal as minutes is one of the most common timesheet errors there is. The converter above works both directions: type a decimal to see hours and minutes, or type hours and minutes to get the decimal your payroll software wants. The rule: minutes ÷ 60 gives the decimal part, so 45 minutes = 0.75.
Counting days rather than hours? The age calculator handles calendar arithmetic - leap years included. Converting between time zones is the time zone converter's job.
Add the minutes first, carry any full 60 into the hours, then add the hours. Ordinary decimal addition gets this wrong because time runs in sixties.
Eight and a half hours, or 8 hours 30 minutes. Subtract any unpaid break to get the payable total.
Each of these has its own page with the exact factor, a reference table and the working shown. The converter above handles any of them too - these exist so the specific answer is one click rather than a search.