Time Duration Calculator: Hours Between Two Times

The duration between two times on the same day is the later time minus the earlier time. Convert both to 24-hour time, subtract the hours and the minutes separately, and borrow 60 minutes when the minutes go negative.

Example: 9:10 AM to 4:45 PM

1. 24-hour time: 09:10 and 16:45.
2. Hours: 16 − 9 = 7. Minutes: 45 − 10 = 35.
3. Duration: 7 hours 35 minutes = 455 minutes = 7.58 hours.

Example across midnight: 10:30 PM to 6:15 AM

1. 24-hour time: 22:30 and 06:15. The end is earlier than the start, so the span crosses midnight.
2. Add 24 hours to the end time: 06:15 becomes 30:15.
3. 30:15 − 22:30 = 7 hours 45 minutes = 7.75 hours.

The calculator applies the midnight rule automatically whenever the end time is earlier than the start time and no dates are given. A 24-hour result is only possible with dates, because identical start and end times without dates are read as zero duration.

12-hour pitfalls

• 12:00 AM is midnight and 12:00 PM is noon; 12:30 AM is half an hour after midnight.
• 9:00 AM to 5:00 AM is 20 hours. If you meant 5:00 PM, the answer is 8 hours.
• Times typed without AM or PM, such as 8 to 5, are ambiguous. When both values are 12 or less and the end would fall before the start, the end is assumed to be PM; the 24-hour display shows which reading was used.

With dates, the duration can exceed 24 hours and is shown as days plus hours and minutes, and as total hours. Count the full days between the dates first, then add or subtract the difference between the clock times.

Example: Monday 8:00 PM to Wednesday 7:30 AM

1. Monday 20:00 to Wednesday 20:00 is 2 full days = 48 hours.
2. Wednesday 07:30 is 12 hours 30 minutes before 20:00, so subtract: 48:00 − 12:30 = 35 hours 30 minutes.
3. Result: 1 day 11 hours 30 minutes, or 35.5 hours.

This is the calculation behind questions such as how many hours until a deadline or how long a multi-day shift rotation lasts. For a deadline, enter the current date and time as the start and the deadline as the end.

The calculator works with the clock times you enter and does not adjust for daylight saving time. On the night clocks spring forward, a shift entered as 11:00 PM to 7:00 AM shows 8 hours although only 7 real hours passed; on the night clocks fall back, the same entry shows 8 hours although 9 passed. Adjust by one hour on those two nights if you need real elapsed time. How such shifts are paid is a matter of employer policy.

The reverse question is what time it will be after a given duration, or what time it was before. Add or subtract the hours and minutes, carry past 60 minutes, and wrap past 24 hours into the next day.

Example: 2:00 PM + 10 h 45 min. 14:00 + 10:45 = 24:45, past the end of the day, so subtract 24 hours: 00:45 the next day, or 12:45 AM. For a shift end time, add the planned hours plus the unpaid break: an 8-hour shift with a 30-minute lunch starting at 7:00 AM ends at 3:30 PM.