Whether you're tracking work hours, timing a workout, or figuring out how long a flight layover is, calculating the duration between two clock times is a task everyone runs into — and one that's easy to get wrong by hand.
Convert to a Single Unit First
The reliable method is to convert both times to total seconds (or minutes) since midnight, then subtract the start from the end. Trying to subtract hours and minutes separately, column by column, is where most manual mistakes creep in — especially when the minutes need to "borrow" from the hours.
A Worked Example
Start time: 9:45 AM, end time: 2:15 PM. Converting to 24-hour totals: 9:45 = 585 minutes since midnight, 14:15 = 855 minutes since midnight. Duration = 855 − 585 = 270 minutes = 4 hours 30 minutes.
Handling Overnight Shifts
If the end time is earlier than the start time — say a shift runs from 10:00 PM to 6:00 AM — the calculation needs to add 24 hours (1,440 minutes) to the end time before subtracting, otherwise you'd get a negative, meaningless result instead of the correct 8-hour duration.
Enter your start and end times into our time duration calculator below and it handles the conversion, borrowing, and overnight edge case automatically.