Time Duration Calculator

Created by Steven Wooding
Reviewed by Dominik Czernia, PhD candidate and Jack Bowater
Last updated: Mar 21, 2022

This time duration calculator allows you to calculate the duration between two times. It accepts either two elapsed times or two clock times, where it supports both the 12-hour and 24-hour time of day formats. The calculator correctly handles time durations that span midnight. As a bonus, this article shows you how to calculate time duration manually, making sure you have a firm understanding of the maths behind the calculator.

After you've finished using this calculator, you might also be interested in our day counter calculator or finding the number of days between two dates.

What is time?

Simplistically, time is the 4th dimension in our Universe, along with the three spatial dimensions of length, width, and height. You could say that time exists so that everything doesn't happen at once. A universe without time wouldn't be a particularly exciting place to live. Time provides separation of events and allows cause and effect to be determined. So that's time sorted, right? Err, no. Not really. Physicists and philosophers are still debating the exact nature of time and how it behaves to this very day.

Fortunately for us, as long as we measure two times in the same inertial frame of reference (a little bit of relativity there), our time duration calculator will work just fine, without knowing exactly what time is.

How to use the elapsed time calculator?

The elapsed time calculator is in the first part of the calculator, found at the top. Enter a start time and an end time, and you will see the duration between those two times. By default, you can enter the times in hours, minutes, and seconds. However, if you click on the units, you can select other time units to suit your needs.

Note that you can enter any two times in this section of the calculator (as long as the end elapsed time is more than the start elapsed time), and there are no restrictions imposed by the 12- or 24-hour time formats. Though if you are interested in the duration between two clock times, the next section of the calculator is just for you.

How to use the clock time calculator?

The second section of the calculator is a clock time calculator. This calculator helps work out the duration between two times during a single day, or overnight. You can choose to either work with the 12-hour clock format (the one we most use in everyday life) or the 24-hour format (which you might encounter when booking a flight, for example). Here's how you use the clock time duration calculator:

  1. Select either the 12-hour or 24-hour time formats.
  2. Enter the start clock time, giving the hour, minute, and optionally second. If you are using the 12-hour clock, don't forget to select whether it is am (in the morning) or pm (afternoon/evening).
  3. Then do the same for the end clock time. The calculator supports time durations that start on one day and end the next day. So you could find the time duration from 8 pm until 5 am the next morning.
  4. The time duration calculator result will be shown as the number of hours, minutes, and seconds between the two times. If you want to see the result in another time unit (e.g., just in seconds), click on the units to display the dropdown menu.

If you need to calculate time durations for a whole week at work, then our time card calculator might be worth checking out.

How to calculate time duration manually?

Let's take some time to discuss how to do these time duration calculations manually. The same principles apply to both the elapsed time calculator and the clock time calculator (though for the clock time calculator, if you are using the 12-hour time format, the first thing to do is to convert it to the 24-hour format. The solution is simply a case of adding 12 hours to any pm times!).

We will first study the example of calculating the time duration between 8:13 am and 4:55 pm. So we first convert the pm time to the 24-hour format:

  • 4:55 pm => 4 + 12 = 16 => 16:55

We can then write down the two times the same way you would do a manual math subtraction:

16:55
-8:13
-----
 8:41

Then calculate the difference in hours and minutes separately. In this example, the result for the number of hours is 16 - 8 = 8 hours, and for the number of minutes, it is 55 - 14 = 41 minutes.

Next, let's look at a more complicated example. How about 8:13 am until 4:07 pm? We convert the pm time to 24-hour clock format as before and write down the subtraction:

16:07
-8:13
------
 8:-06 ??? Not a valid time.

On this occasion, however, if we try to do the subtraction on the minutes' column, we would end up with minus 6. In this case, we need to convert an hour from the hours' column to 60 minutes in the minutes' column so we can get a positive value for the time difference. Here is what the new manual subtraction looks like:

15:67
-8:13
-----
 7:54

So 16 hours became 15 hours, and 7 minutes became 67 minutes, when we added the 60 minutes, carried over from the hours' column. Now we can do the subtraction for the hours 16 - 8 = 7 hours and minutes 67 - 13 = 54 minutes as before. This same carryover method can be used if we also had a seconds' column.

Finally, if you want to calculate a time difference from one day to the next, you would need to add a day column and carryover 24 hours (as it is a day in the future), adding it to the hours column of the first time. For example, to find the duration between 4:07 pm until 8:13 am the next morning, you would do:

 1 day 8:13     ->     32:13
-0 day 16:07          -16:07
------------          ------
                       16:06

So for some clock times, calculating the duration between two times is a little tricky, so it might be better to use our calculator instead!

FAQ

How do I calculate time duration?

To calculate the time duration between two times:

  1. Write both times in 24-hour format.
  2. Write the later time above the earlier time and perform a long subtraction with some additional caveats:
    • If you need to carry over from the hours into the minutes column, be sure to add 60 minutes and not 100 minutes.
    • If the time duration happens on different days, add a left-most 'days' column. If you need to carry over from the days column into the hours column, be sure to add 24 hours.

How do I write time duration?

There is no set way to write time duration. If you need to write the time in shorthand, then the hh:mm:ss format will likely be enough (you can add more columns, such as days or milliseconds, as you see fit). You could also write out the time duration explicitly in words, if you so desired, e.g., 1 hour, 26 minutes, and 49 seconds.

How do I determine the duration of time intervals in hours?

To find the duration of a time interval in hours:

  1. Write both times in their 24-hour forms.
  2. Subtract the earlier time from the later time.
  3. If you have any amount of minutes or seconds left after subtraction:
    1. Divide the seconds by 60 and add this value to the minutes.
    2. Divide the minutes by 60 and add this to the total hours.
  4. If you have any days, multiply the number of days by 24 and add this to the remaining hours.

What is 12:30 am in 24hour format?

12:30 am is 00:30 in 24-hour format. This is because it is the first 30 minutes of the day.

Steven Wooding
Elapsed time duration calculator
Start time
hrs
min
sec
End time
hrs
min
sec
Duration
hrs
min
sec
Clock time duration calculator
Clock format
12-hour
Start clock time:
Am or pm
am
Hour
hrs
Minute
mins
Second
secs
End clock time:
Am or pm
am
Hour
hrs
Minute
mins
Second
secs
Clock duration
hrs
min
sec
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