How to add and subtract time
Time uses base 60, not base 10, which is why it's easy to slip up on paper. To add 1:45 and 2:30, add the minutes (45 + 30 = 75), carry 60 minutes over as one hour (1 hour 15 minutes), then add the hours: 1 + 2 + 1 = 4 hours 15 minutes.
To subtract, borrow 60 minutes from the hours when needed: 5:10 − 2:40 → 4:70 − 2:40 = 2 hours 30 minutes.
Converting to decimal hours
Payroll and invoicing often need decimal hours. Divide the minutes by 60: 7 hours 45 minutes = 7 + 45/60 = 7.75 hours. The total above shows the decimal value automatically.
| Minutes | Decimal hours |
|---|---|
| 15 | 0.25 |
| 20 | 0.33 |
| 30 | 0.50 |
| 40 | 0.67 |
| 45 | 0.75 |
Overnight times
In "time between two times", if the end time is earlier than the start time the calculator assumes it is on the next day — so 10:00 PM to 6:00 AM is 8 hours.