How to Calculate Time Differences

Working out how long something took sounds simple, but minutes come in sixties and days wrap around at midnight. Here's a method that works every time.

Within the same day

Subtract the minutes, then the hours. To find the time from 9:15 to 14:40:

• Minutes: 40 − 15 = 25
• Hours: 14 − 9 = 5
• Result: 5 hours 25 minutes

Use 24-hour time for this, because it removes the AM and PM step. If you need help with that, see what the 24-hour clock is.

When you need to borrow

If the minutes come out negative, borrow an hour. From 9:50 to 14:20:

• Minutes: 20 − 50 is negative, so borrow 1 hour and use 80 − 50 = 30
• Hours: 14 − 9 − 1 = 4
• Result: 4 hours 30 minutes

Across midnight

Split the calculation at midnight. From 22:30 to 06:15 the next day:

• 22:30 to 24:00 is 1 hour 30 minutes
• 00:00 to 06:15 is 6 hours 15 minutes
• Total: 7 hours 45 minutes

Across time zones

To find how long a flight really takes, convert both times to the same zone first. A flight leaves New York at 19:00 and lands in London at 07:00 the next day. London is usually 5 hours ahead, so landing at 07:00 London time is 02:00 in New York. From 19:00 to 02:00 is 7 hours.

The time zone converter does the conversion for you, including daylight saving changes. For whole days rather than hours, use the date calculator.

Daylight saving days

On the days clocks change, a day has either 23 or 25 hours in many places. If an overnight shift crosses a change, the wall-clock difference will be an hour off from the time actually worked, so check the date.