Working with Elapsed Time

Excel allows you to enter many things into a cell, including times. This leads some people to use Excel to help calculate elapsed times. For instance, you may have a column that contains a starting time, another that contains an ending time, and then use a third column to calculate the time between the beginning and ending time.

In such situations, you may be tempted to simply put the following as your formula in the cells of the third column:

=B2-A2

This will work fine, provided the time shown in B2 is always later than the time shown in A2. However, you will get erroneous results if the times do not fit this rigid stricture. What do you do if you are running operations around the clock, and it is just as likely that the value at A2 will be just before midnight and the value in B2 will be after midnight?

One solution is to make sure that you always enter dates with your times. If you do this, then B2 will always be later than A2. For many people, however, this is a bother. If you find yourself simply entering the time, then you are still up the creek.

If you enter your times without an AM/PM designation using a 12-hour clock, then you should use the following formula in the cells of the third column:

=IF(A2>B2,(B2+0.5)-A2,B2-A2)

This formula uses the IF function to determine if the beginning time is later than the ending time. If it is, then .5 (which is half a day, or 12 hours) is added to the ending time before the subtraction is done. If the beginning time is earlier then the ending time, then a normal subtraction operation is done.

If you use an AM/PM designation in your times, or you enter information using a 24-hour clock, then the formula must change just a bit. Now it should appear as follows:

=IF(A2>B2,(B2+1)-A2,B2-A2)

Now, instead of adding only half a day, you are adding a whole day (24 hours) to the ending time. This, again, provides the proper result.

It is interesting to note that in both of these instances, Excel allows you to add hours and minutes, if desired. While the above example is clean and simple, the following could also have been used:

=IF(A19>B19,(B19+"24:00")-A19,B19-A19)

Regardless of the formula you use, once it is entered you need to make sure the cell with the formula is formatted to properly show elapsed time. You do this by following these steps:

1. Display the Format Cells dialog box. (Click here to see a related figure.) In versions of Excel prior to Excel 2007, choose Cells from the Format menu. In Excel 2007 press Ctrl+1.
2. In the Category list (left side) choose Time.
3. In the Type box, choose 37:30:55 as the type.
4. Click on OK.

Your cell now shows the correct elapsed hours, minutes, and seconds.