How to Add and Subtract Hours and Minutes Without Mistakes
October 21, 2026
Hours and minutes work in base 60, so you cannot add them like ordinary decimals. Add the minutes separately, carry any total of 60 or more into the hours, then add the hours. For 2 h 45 min + 1 h 30 min + 3 h 50 min, the hours sum to 6 and the minutes to 125, which is 2 h 5 min, giving a total of 8 h 5 min.
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Add the minutes first: 45 + 30 + 50 = 125. Divide by 60: 125 = 2 × 60 + 5, so write down 5 minutes and carry 2 hours. Add the hours: 2 + 1 + 3 + 2 (carried) = 8. The total is 8 hours 5 minutes.
For clock times, add the duration to the start time and roll past 12 or 24 as needed: 9:40 plus 2 h 35 min is 12:15.
Subtracting Times
When the minutes of the first time are smaller than the minutes of the second, borrow one hour as 60 minutes. For 5 h 20 min − 2 h 45 min, borrow: 4 h 80 min − 2 h 45 min = 2 h 35 min.
To find the time between 8:50 a.m. and 2:15 p.m., convert to 24-hour time (8:50 and 14:15), then subtract: 13 h 75 min − 8 h 50 min = 5 h 25 min.
The Decimal Hours Trap
A very common mistake is reading 7.30 hours as 7 hours 30 minutes. In decimal hours, 7.30 hours is 7 hours and 18 minutes (0.30 × 60). To convert minutes to decimal hours, divide by 60: 45 minutes is 0.75 hours and 20 minutes is 0.33 hours.
Timesheets that need decimal hours for payroll should be converted carefully. A shift of 8 h 20 min is 8.33 hours; at $18 an hour, pay is about $149.94.
| Minutes | Decimal hours |
|---|---|
| 6 | 0.10 |
| 15 | 0.25 |
| 30 | 0.50 |
| 45 | 0.75 |
| 50 | 0.83 |
Crossing Midnight and Time Zones
When a shift goes past midnight, add 24 hours to the end time before subtracting. A shift from 10:30 p.m. to 6:15 a.m. is 30:15 − 22:30 = 7 h 45 min.
For time zones, convert to a common reference such as UTC first, do the arithmetic, then convert back, so daylight saving shifts do not trip you up.
Frequently Asked Questions
How do I add hours and minutes together?
Add the minutes, carry every 60 into the hours, then add the hours.
What is 7.5 hours in hours and minutes?
7 hours 30 minutes, since 0.5 × 60 = 30.
How do I subtract time when the minutes are smaller?
Borrow one hour, which gives 60 more minutes, then subtract as usual.
How do I calculate the time worked across midnight?
Add 24 hours to the end time, then subtract the start time.