Adding 2 hours 45 minutes to 1 hour 30 minutes is not like adding normal numbers, because time works in 60s, not 100s. Many timesheet and travel mistakes come from this. This guide shows how to add and subtract time correctly, with examples, and how our free Time Calculator does it instantly.
Adding time
Add seconds, then minutes, then hours. Whenever seconds or minutes reach 60, carry 1 to the next unit.
Example: 2 h 45 min + 1 h 30 min
- Minutes: 45 + 30 = 75 minutes = 1 hour 15 minutes
- Hours: 2 + 1 + 1 (carried) = 4
- Result: 4 h 15 min
Subtracting time
Subtract seconds, then minutes, then hours. If the top number is smaller, borrow 60 from the next unit.
Example: 5 h 10 min − 2 h 35 min
- 10 minutes is less than 35, so borrow 1 hour: 70 − 35 = 35 minutes
- Hours: 4 − 2 = 2
- Result: 2 h 35 min
Time between two clock times
From 9:40 to 17:15:
- From 9:40 to 17:40 is 8 hours
- 17:15 is 25 minutes earlier, so 7 h 35 min
If the end time is after midnight, add 24 hours to it first. From 22:30 to 06:15 next morning: 06:15 + 24:00 = 30:15, minus 22:30 = 7 h 45 min.
Decimal hours
Payroll and billing often use decimal hours. Divide minutes by 60:
| Time | Decimal hours |
|---|---|
| 15 min | 0.25 |
| 30 min | 0.5 |
| 45 min | 0.75 |
| 7 h 20 min | 7.33 |
Never write 7 h 20 min as 7.20 hours; that would be 7 h 12 min. Our guide on decimal hours explains this in detail.
Adding a list of times
For a week of work shifts, add all hours and minutes separately, then convert extra minutes to hours. The Working Hours Calculator is built for timesheets, including breaks and overtime.
12-hour vs 24-hour
Mixing AM/PM can cause errors. Convert to 24-hour time first with the 12h / 24h / Military Time Converter, then calculate.
Frequently asked questions
How do I add hours and minutes?
Add minutes and hours separately, and carry 1 hour for every 60 minutes.
How do I calculate time across midnight?
Add 24 hours to the end time before subtracting.
Is 7.5 hours the same as 7 hours 50 minutes?
No. 7.5 hours is 7 hours 30 minutes.