How to add and subtract hours and minutes
Calculate clock times and durations without treating minutes like ordinary base-10 decimals.
Add durations in two columns
Add the minute amounts first. If the result is 60 or more, convert each group of 60 minutes into one hour. Then add that extra hour to the hour column.
For 3:50 plus 2:25, the minutes equal 75. That is 1 hour 15 minutes. The original hours total five, plus the carried hour, producing 6 hours 15 minutes.
Subtract by borrowing one hour
When the ending minute number is smaller than the minutes you need to subtract, borrow one hour and convert it to 60 minutes. To subtract 1:45 from 4:20, rewrite 4:20 as 3:80. Then 80 − 45 = 35 minutes and 3 − 1 = 2 hours, giving 2:35.
Find elapsed time across noon or midnight
Break the interval at an easy boundary. From 10:45 a.m. to 1:20 p.m., the time to noon is 1 hour 15 minutes, and noon to 1:20 is 1 hour 20 minutes. Together they equal 2 hours 35 minutes.
Across midnight, calculate the time to midnight and then add the time after midnight. From 10:30 p.m. to 1:15 a.m. is 1 hour 30 minutes plus 1 hour 15 minutes, or 2 hours 45 minutes.
Avoid decimal-time mistakes
Clock minutes use base 60, not base 100. Two hours 30 minutes is 2.5 decimal hours, not 2.30 hours. If a payroll system uses decimals, convert the minute portion by dividing it by 60.
- 15 minutes = 0.25 decimal hours
- 30 minutes = 0.50 decimal hours
- 45 minutes = 0.75 decimal hours
Frequently asked questions
What is 1 hour 50 minutes plus 35 minutes?
The minutes total 85, or 1 hour 25 minutes. The full result is 2 hours 25 minutes.
How do I subtract 40 minutes from 2:15?
Borrow one hour and write 2:15 as 1:75. Subtract 40 minutes to get 1:35.
Is 2 hours 15 minutes equal to 2.15 hours?
No. Fifteen minutes is 0.25 hours, so the decimal value is 2.25 hours.
Published August 3, 2026 · Reviewed for clarity and source accuracy.