Time Duration Calculator

About this Time Duration Calculator

The Time Duration Calculator measures elapsed time between two clock times. If the end time is earlier than the start time, it assumes the interval crosses midnight, which makes it useful for shifts, travel and event timing.

Finding the elapsed time between two clock times seems simple until the calculation crosses midnight or spans a shift that starts in the evening and ends the next morning, both of which require subtracting across a day boundary.

For related tasks, try Hours & Minutes to Decimal, Decimal Hours to Time or Work Hours Calculator.

How the calculation works

Both times are converted to minutes after midnight. When the end is earlier, 24 hours are added to the end before subtraction.

How to use it

1. Enter the start time.
2. Enter the end time.
3. Calculate to see total minutes and hours/minutes.

Practical example

From 22:30 to 01:15, the calculator treats the interval as overnight and returns 2 hours 45 minutes.

A shift starting at 11:30 PM and ending at 7:15 AM the next day spans exactly 7 hours and 45 minutes, a duration that would be calculated incorrectly as a negative number by naive subtraction unless the midnight crossing is properly accounted for.

Things to double-check

When a time range crosses midnight, such as a shift from 10 PM to 6 AM, the calculation must add 24 hours conceptually to the end time before subtracting, since a simple subtraction would otherwise produce a negative or incorrect duration; this tool handles that adjustment automatically.

Finding elapsed time

Elapsed time is the end time minus the start time. From 9:15 to 17:45 is 8 hours and 30 minutes. When the end is earlier than the start, the span crosses midnight: 22:30 to 06:15 is 7 hours and 45 minutes, found by adding 24 hours to the end time. The calculator handles the overnight case. Convert the result to decimals, 7.75 hours here, when you need it for payroll.

12-hour and 24-hour clocks

Many errors come from AM and PM. 12:00 AM is midnight and 12:00 PM is noon, so 11:30 PM to 1:15 AM is 1 hour and 45 minutes. The 24-hour clock avoids the confusion, with 23:30 to 01:15. If you enter times in 12-hour format, double check AM and PM. For long durations over a day, use the Date Difference Calculator.

Breaks and multiple shifts

To find paid time, subtract unpaid breaks from the total. A shift from 8:00 to 16:30 with a 30 minute unpaid break is 8 hours of work. For several shifts in a day, calculate each separately and add. Keep track of whether breaks are paid, since rules differ by employer and country. Record start and end times on the day, as memory is unreliable.

Other uses

Duration calculations are useful for travel times, flights, cooking schedules, study sessions and equipment logs. For a flight, remember that departure and arrival times are in local time zones, so subtract the time difference to get the real flight time. A flight leaving at 08:00 and landing at 12:30 local time in a city that is 3 hours behind lasts 7 hours and 30 minutes, because 12:30 there is 15:30 in the departure city.

Adding several durations

To add durations, add the hours and the minutes separately and carry over from minutes to hours. 2 hours 45 minutes plus 1 hour 30 minutes plus 3 hours 50 minutes gives 6 hours and 125 minutes, which is 8 hours 5 minutes. This is how you total the time spent on several tasks or the length of a multi-leg journey. Convert the final answer to decimals if you need it for billing, which gives 8.08 hours.

Worked example: a night shift

A shift runs from 21:45 to 06:20 the next morning. From 21:45 to midnight is 2 hours 15 minutes, and from midnight to 06:20 is 6 hours 20 minutes, so the total is 8 hours 35 minutes. With an unpaid break of 45 minutes, the paid time is 7 hours 50 minutes, which is 7.83 in decimal hours. The calculator does this automatically when the end time is earlier than the start time, but it helps to understand the steps, so that you can check payslips and rosters yourself.

Trips, flights and layovers

Travel times need care because local clocks differ between places. A flight that leaves at 07:10 and lands at 13:55 local time in a city three hours behind the departure city shows 6 hours 45 minutes on the clock face, but because the arrival clock is three hours behind, you add three hours, so the flight lasts 9 hours 45 minutes. Add the time of connections, check-in and transfers to find the full journey time. For trains and buses, subtract the departure time from the arrival time in the same time zone. Keep a note of both local times and the time difference to avoid errors.

Adding up lap and task times

Durations often need adding. Three laps of 4:12, 4:09 and 4:15 add to 12:36, an average of 4:12 per lap. To add, convert each to seconds, which is 252, 249 and 255, total 756, then convert back to 12 minutes and 36 seconds. The same approach works for the time spent on tasks in a day or the length of several recordings. Take care when minutes pass 60 and seconds pass 60, since you need to carry over to the next unit.

Clock changes and common mistakes

On the night that clocks go back, a shift from 22:00 to 06:00 lasts 9 hours, and on the night they go forward it lasts 7. Other common mistakes are mixing AM and PM, forgetting that 12:00 AM is midnight and entering minutes as decimals. When a duration looks odd, calculate it in a second way, such as counting up to the next whole hour and then the rest. For long periods that span days, use the Date Difference Calculator along with this tool.

Key terms explained

Elapsed time is the time that passes between a start and an end. A duration is the length of a period of time. The 12-hour clock uses AM and PM, while the 24-hour clock counts from 00:00 to 23:59. Midnight is 00:00 and noon is 12:00. An overnight shift crosses midnight. A break is a pause that may be paid or unpaid. Daylight saving time moves the clock by an hour in some places, which changes the length of the night on the day of the change.

Rules of thumb and quick checks

To find the time from a start to an end on the same day, subtract the times. If the end is earlier than the start, add 24 hours to the end. Count up to the next whole hour and add the rest as a check. For example, from 9:40 to 13:15 is 20 minutes plus 3 hours 15 minutes, which is 3 hours 35 minutes. Use the 24-hour clock to avoid mistakes with AM and PM.

Quick reference and sanity checks

To check a duration, subtract the earlier time from the later one, borrowing 60 minutes when the minutes of the later time are smaller. For example, from 9:45 to 14:20 is 4 hours and 35 minutes. When the end time is earlier than the start time, the period crosses midnight and one day must be added, so 23:30 to 01:15 is 1 hour and 45 minutes. Use the 24-hour clock to avoid mistakes between AM and PM. Remember that daylight saving changes can add or remove an hour on some dates, and that the tool measures clock time, not working time with breaks.

Frequently asked questions