Time Calculator
Add or subtract two durations, or convert a duration into total seconds, minutes, hours and days. No sign-up, nothing sent to a server.
How time arithmetic actually works
Times are not decimals. 1.5 hours is 1 hour 30 minutes, but 1.50 in the hh:mm:ss sense means 1 hour 50 minutes — the fractional part counts in sixties, not hundredths. That mismatch is the single most common source of payroll and timesheet errors.
The safe method is to convert everything to seconds, do the arithmetic, then convert back. This calculator does exactly that, which is why 45 minutes plus 45 minutes gives 1:30:00 and not 1:90:00.
Subtraction can produce a negative result — for example when the second duration is longer than the first. The result is shown with a minus sign rather than wrapped around, because a negative duration usually means the inputs were entered the wrong way round.
Where you actually need this
Timesheets. Six start/end pairs a day, each with a lunch break. Adding them by hand invites the sixties carry error; adding total minutes and dividing by 60 at the end is safer.
Audio and video editing. Clip lengths are given in mm:ss or hh:mm:ss and have to sum to a target runtime. Rounding each clip before adding drifts by seconds per clip.
Training and billing. Sessions logged as 1:20, 0:45, 2:10 should total 4:15, not 3.75 in decimal hours — unless you are billing in decimal, in which case convert after summing.
Decimal hours versus clock time
Payroll systems often want decimal hours: 1:30 becomes 1.50, 1:45 becomes 1.75. To convert, divide the minutes by 60 — but do it once at the end, on the total, not per entry. Rounding each entry to two decimals and then summing can shift a full hour over a month.
The converter tab shows both: the clock form and the decimal form, so you can copy whichever your system expects.
Frequently asked questions
How do I add hours and minutes correctly?
Convert both durations to the same unit first. Adding minutes separately and carrying every 60 into hours is the manual method; this tool converts to seconds, adds, then converts back.
Why is 1.5 hours not 1 hour 50 minutes?
Because decimal hours and clock time use different bases. 1.5 decimal hours = 90 minutes = 1:30:00. 1:50 is 1.83 decimal hours.
Can the result be negative?
Yes, when you subtract a longer duration from a shorter one. It is shown with a minus sign — usually a sign the two inputs are swapped.
Does it handle more than 24 hours?
Yes. Durations are not wrapped at 24 hours, so 30 hours stays 30:00:00 rather than becoming 6:00:00.
Is anything sent to a server?
No. All arithmetic runs in your browser; the page works offline once loaded.
How do I convert to decimal hours for payroll?
Use the converter tab and read the 'total hours' value — it is already decimal (1:30 → 1.5).