Time Calculator

Adding and subtracting times is fiddly because there are 60 minutes in an hour, not 100, so ordinary arithmetic gives wrong answers. This calculator handles time properly: add two durations, subtract one from another, or find the gap between two clock times, in 12-hour or 24-hour format.

People use it to add up durations — total runtime of several recordings, combined task times — or to work out how far apart two moments are. The result comes back both as hours, minutes, and seconds and as decimal totals, which is handy when you need to feed the figure into something else, such as a timesheet that expects decimal hours or a spreadsheet formula that works in plain seconds.

Adding or subtracting durations by hand goes wrong because the units are not decimal: sixty seconds carry into a minute and sixty minutes into an hour, so borrowing and carrying happen at 60 rather than 10. The tool sidesteps that entirely by converting both operands to a total in seconds, doing plain arithmetic, then converting back.

That approach makes results exact rather than approximate, and it is why the tool can also express the same duration as a decimal number of hours or minutes. Those decimal forms are what timesheets and billing systems usually want — three hours and forty-five minutes is 3.75 hours, not 3.45.

Subtraction can produce a negative duration where the second value is larger. That is a legitimate answer rather than an error: it represents a deficit, which is exactly what you want when comparing a target time against an actual one.

A duration is an elapsed quantity and a time of day is a position on a clock, and the distinction matters for what can sensibly be done to each. Adding two durations is meaningful; adding two times of day is not. Adding a duration to a time of day is meaningful, and gives another time of day — possibly on the following calendar day, which is where shift calculations across midnight go wrong.

Decimal conversion is the most common practical need, and the mistake is reading the minutes as a decimal fraction directly. Fifteen minutes is 0.25 hours, thirty is 0.5, and forty-five is 0.75; anything else needs dividing by sixty. Payroll systems generally expect decimal hours, so the conversion is worth getting right.

Two things this arithmetic deliberately ignores. Rounding conventions vary by employer — some round to the nearest quarter hour, which can favour either party — and time zones and daylight saving affect times of day but never durations. An eight-hour shift is eight hours regardless of a clock change; the times it starts and ends are what shift.