How to Calculate the Hours Between Two Times

Calculating the duration between two times can be tricky, especially if the times cross over the noon threshold (AM to PM) or cross midnight into the next day.

1. Convert to a 24-Hour Clock

The easiest manual method is to convert both times to military time (a 24-hour clock). To do this, simply add 12 to any PM time. For example, 3:00 PM becomes 15:00.

2. Subtract the Times

Once both times are in a 24-hour format, subtract the start time from the end time.

Example: You start at 9:15 AM (09:15) and end at 3:45 PM (15:45).

15 hours - 9 hours = 6 hours
45 minutes - 15 minutes = 30 minutes
Total: 6 hours and 30 minutes.

3. What if the start minutes are higher than the end minutes?

If you start at 9:45 AM and end at 3:15 PM (15:15), you cannot subtract 45 from 15 easily. You must "borrow" an hour. Change 15:15 into 14:75 (by taking away 1 hour and adding 60 minutes). Now you can subtract:

14 hours - 9 hours = 5 hours
75 minutes - 45 minutes = 30 minutes
Total: 5 hours and 30 minutes.

Overnight Shifts

If your shift crosses midnight (e.g., 10:00 PM to 6:00 AM), simply add 24 hours to your end time before subtracting. So 6:00 AM becomes 30:00. Then subtract 22:00 (10:00 PM) to get exactly 8 hours.