Time Calculator
Add and subtract hours, minutes and seconds. Or work out the time between two clock times.
What are you working out?
First time
Second time
This adds and subtracts times and durations, and finds the elapsed time between two clock times.
It also converts between hours-and-minutes and decimal hours, which payroll uses.
How time arithmetic works
Time arithmetic trips people up for one reason: minutes are base 60, not base 100. Every mistake in this area comes from treating them as decimals.
2:45 + 3:30 is not 5:75. Add the minutes to get 75, carry an hour, and the answer is 6:15. The same applies to elapsed time: from 9:15 AM to 5:30 PM is 8 hours 15 minutes, or 495 minutes.
The conversion that matters most is to decimal hours, because that is what payroll systems use. 8 hours 15 minutes is 8.25 hours, not 8.15. Fifteen minutes is a quarter of an hour, so it is 0.25 — and getting this wrong on every timesheet costs real money.
Converting everything to minutes first makes addition trivial. Dividing minutes by 60 gives the decimal figure payroll expects.
What to enter
- Times or durations
- Clock times such as 9:15 AM, or durations such as 2 hours 45 minutes. The tool handles both.
- Operation
- Add, subtract, or find the elapsed time between two clock times.
- Output format
- Hours and minutes, total minutes, or decimal hours for payroll.
Minutes to decimal hours
- 15 minutes
- 0.25 hours.
- 20 minutes
- 0.33 hours.
- 30 minutes
- 0.50 hours.
- 45 minutes
- 0.75 hours.
- The rule
- Divide minutes by 60. 10 minutes is 0.167, not 0.10.
What this assumes
Elapsed times crossing midnight need a date, or the calculation has to assume the next day.
Daylight saving transitions make some days 23 or 25 hours long, which affects durations spanning them.
How to calculate time calculations
Convert everything to minutes, do the arithmetic, then convert back.
- converting back
- Hours = total ÷ 60, minutes = the remainder
- decimal hours
- What payroll and billing systems use
Convert each time to minutes. 2:45 is (2 × 60) + 45 = 165 minutes. 3:30 is 210.
Add or subtract. 165 + 210 = 375 minutes.
Convert back to hours and minutes. 375 ÷ 60 = 6 remainder 15, so 6:15.
For payroll, divide the minutes by 60. 8 hours 15 minutes is 8 + (15 ÷ 60) = 8.25 decimal hours.
See a worked example: a working day, three ways
- Start
- 9:15 AM
- End
- 5:30 PM
In 24-hour terms: 17:30 − 9:15.
As minutes: 1,050 − 555 = 495 minutes.
As hours and minutes: 495 ÷ 60 = 8 hours 15 minutes.
As decimal hours for payroll: 8.25. Writing 8.15 on a timesheet under-reports by 6 minutes a day, which is about 26 hours a year.
8 hours 15 minutes, or 8.25 decimal hours
Frequently asked questions
Divide by 60. 15 minutes is 0.25 hours, 30 is 0.50, and 45 is 0.75.
The common error is treating minutes as hundredths. 8 hours 15 minutes is 8.25, not 8.15, and the difference compounds across a pay period.
Because minutes roll over at 60, not 100. 2:45 + 3:30 gives 75 minutes, which carries an hour and leaves 15, so 6:15 rather than 5:75.
Converting everything to total minutes first removes the problem entirely, then convert back at the end.
Add 24 hours to the end time before subtracting. A shift from 10:00 PM to 6:00 AM is 30:00 − 22:00 = 8 hours.
Any tool handling shift work needs to do this. Without it, an overnight shift returns a negative duration.
The 24-hour clock: 1:00 PM is 13:00, midnight is 00:00, and there is no AM or PM.
It is unambiguous, which is why it is used in medicine, aviation and the military. It also makes time arithmetic easier, since you never have to convert across noon.
Many round to the nearest quarter hour. Under US Department of Labor rules, rounding is permitted provided it is neutral over time and does not consistently favour the employer.
So 8:07 might round to 8:00 and 8:08 to 8:15. What is not permitted is rounding down only.
Yes, for anything spanning a transition. The spring-forward day is 23 hours long and the autumn day is 25.
An overnight shift across a transition is genuinely an hour shorter or longer, and payroll practice on this varies by employer.
Problems people actually run into
Writing 8.15 instead of 8.25
Eight hours fifteen minutes is 8.25 decimal hours. Writing 8.15 treats minutes as hundredths and under-reports by six minutes.
At five days a week that is 26 hours a year, unpaid. Divide minutes by 60, every time.
Adding times without carrying
2:45 + 3:30 = 5:75 is a valid-looking answer that cannot exist, since no clock reads 75 minutes.
Convert to total minutes, add, then convert back. It takes one extra step and removes the whole class of error.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: September 4, 2026