Time between two times
Duration = end − start (+ 24 h if end is earlier than start) − break Decimal hours = hours + minutes ÷ 60
If the end time is earlier than the start time, the calculator assumes the shift ends the next day. For example, 10:00 PM to 6:00 AM is 8 hours. Equal start and end times give zero.
Decimal hours are what most payroll systems use: 7 hours 45 minutes is 7.75 hours, because 45 ÷ 60 = 0.75.
How to work out hours by hand
Take a shift from 8:45 AM to 5:15 PM with a 30-minute unpaid lunch:
- Convert both times to the 24-hour clock: 8:45 and 17:15.
- Subtract: 17:15 − 8:45. Borrow an hour because 15 minutes is less than 45, giving 16:75 − 8:45 = 8 h 30 min.
- Take off the break: 8 h 30 min − 30 min = 8 h 0 min.
- Convert to decimal: 8 + 0 ÷ 60 = 8.00 hours.
For an overnight shift, add 24 hours to the end time first. 10:00 PM to 6:30 AM becomes 22:00 to 30:30, which is 8 h 30 min; with a 30-minute break that's 8.00 hours.
Example weekly time card
| Day | Start | End | Break | Hours worked | Decimal |
|---|---|---|---|---|---|
| Mon | 8:30 AM | 5:00 PM | 30 min | 8 h 0 min | 8.00 |
| Tue | 8:45 AM | 5:15 PM | 30 min | 8 h 0 min | 8.00 |
| Wed | 9:00 AM | 6:00 PM | 45 min | 8 h 15 min | 8.25 |
| Thu | 7:50 AM | 4:20 PM | 30 min | 8 h 0 min | 8.00 |
| Fri | 8:00 AM | 12:30 PM | None | 4 h 30 min | 4.50 |
| Total | 36 h 45 min | 36.75 |
Add up the minutes first, then convert the total to decimal. Adding rounded daily decimals can drift by a few hundredths over a week.
Minutes to decimal hours
| Minutes | Decimal | Minutes | Decimal |
|---|---|---|---|
| 5 | 0.08 | 35 | 0.58 |
| 10 | 0.17 | 40 | 0.67 |
| 15 | 0.25 | 45 | 0.75 |
| 20 | 0.33 | 50 | 0.83 |
| 25 | 0.42 | 55 | 0.92 |
| 30 | 0.50 | 60 | 1.00 |
A common timesheet mistake is writing 8 h 30 min as 8.30. That's 8 hours and 18 minutes; the correct decimal is 8.50.
Adding and subtracting durations
Total seconds = hours × 3,600 + minutes × 60 + seconds
Both durations are turned into seconds, added or subtracted, then turned back into hours, minutes and seconds. Minutes and seconds above 59 carry over, so 90 minutes becomes 1:30:00.
For example, 1:45:30 + 2:30:45 = 4:16:15, and 3:10:00 − 1:25:30 = 1:44:30. This is handy for adding up lap times, video clips or time spent on a project.