Time Calculator
Add or subtract two lengths of time and the time calculator carries 60 seconds into a minute, 60 minutes into an hour and 24 hours into a day.
Total
- As hours:minutes:seconds Hours are not rolled into days here, which is how a timesheet or a race total is written.
- 6:16:15
- In decimal hours Total seconds divided by 3,600. This is the form an hourly rate multiplies.
- 6.2708333 h
- In minutes
- 376.25 min
- In seconds
- 22,575 s
- In days
- 0.26128472 days
- Working Each time is converted to seconds (days × 86,400 + hours × 3,600 + minutes × 60 + seconds), the seconds are added or subtracted, and the total is split back into units.
- 3 h 45 min 30 s = 13,530 s; 2 h 30 min 45 s = 9,045 s; 13,530 + 9,045 = 22,575 s = 6 h 16 min 15 s
How the Time Calculator works
To add or subtract times, convert each one to seconds, do the arithmetic, and convert back. The formula is total seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds. To convert back, divide by 3,600 for the hours, divide what is left by 60 for the minutes, and the remainder is the seconds.
Worked example: 3 h 45 min 30 s + 2 h 30 min 45 s. The first time is 3 × 3,600 + 45 × 60 + 30 = 13,530 seconds and the second is 2 × 3,600 + 30 × 60 + 45 = 9,045 seconds. Together they make 22,575 seconds. 22,575 ÷ 3,600 = 6 with 975 left over, and 975 ÷ 60 = 16 with 15 left over, so the total is 6 h 16 min 15 s.
On paper the same sum goes column by column, carrying at 60 instead of 10. Seconds: 30 + 45 = 75, which is 1 minute 15 seconds, so write 15 and carry 1. Minutes: 45 + 30 + 1 = 76, which is 1 hour 16 minutes, so write 16 and carry 1. Hours: 3 + 2 + 1 = 6. Adding the digits as if they were decimals is the usual slip: 1:45 plus 0:30 is 2:15, and 1:75 is a time that does not exist.
Decimal hours are total seconds divided by 3,600. The example is 22,575 ÷ 3,600 = 6.2708 hours. That is the figure to multiply by an hourly rate, and it is why 6 h 16 min is about 6.27 hours on a timesheet and never 6.16.
Hours past 24 roll into days: 20 h + 9 h is 1 day 5 h. Shown without days, the same total is 29:00:00.
Time Calculator FAQ
How do I subtract times by hand?
Subtract the seconds, then the minutes, then the hours, borrowing 60 from the next column when the top number is smaller. For 5 h 10 min - 2 h 45 min, borrow an hour as 60 minutes: 4 h 70 min - 2 h 45 min = 2 h 25 min.
How many seconds are in a day?
86,400: 24 hours × 60 minutes × 60 seconds. A week is 604,800 seconds and an hour is 3,600.
What is 90 minutes in hours and minutes?
1 hour 30 minutes, or 1.5 hours: one full 60 minutes and 30 left over.
Can I add a duration to a time of day?
Yes: 9:30 AM plus 3 h 45 min is 1:15 PM, and past midnight the clock starts again at 12:00 AM. For the time between two clock times, such as a 9:00 to 5:30 shift, use the hours calculator.