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MS Office: Calculating Time Difference in Excel

Carlos from Arizona asks:

I need to keep track of my time for a project, but whenever I try to autosum I get a formula error.  Is there a way to calculate time in Excel?

Yes there is, Carlos.  Glad that you asked.

There are many reasons why you may need to keep track of your time on an Excel spreadsheet.  Could be a project like Carlos.  Maybe you’re paying people for work and want to keep time sheets on Excel.  Perhaps, like me, you’re a freelance writer who needs to track personal vs work time on the PC for the IRS.  For whatever reason you need to do it, though, it is possible and even fairly easy once you get the hang of it.

The first thing you need to decide is how you’re going to format your time, by a twelve or twenty-four hour clock.  For anyone who doesn’t know, the difference is that on a twelve hour clock 10:03 at night would be typed “10:03 PM”, whereas on a twenty-four hour clock it would be “2203” or “22:03″.  I know that sounds fairly elementary, but I still run in to people who don’t know how to read or write 24 hour time. It doesn’t really matter which you choose, I would just recommend choosing one and sticking to it for your own convenience.

Now it comes time to enter your times.  Key your start times in one column and your end times in the next, leaving room for your formula in the third, thusly:

For your formula for, for instance, row 41, you would want to enter =c41-b41.  It’s possible that Excel will format this correctly the first time.  If it doesn’t, then simply pull up your format cells window by right-clicking on the cell and then clicking “format cells”.

Then click on the “number” tab if it’s not already there, and then on “custom” in the window on the right.  Scroll down until you find “h:mm”.

And voila – you have your time calculation.

When you want to add the column of totals, you can use the autosum feature, just make sure that you format the total cell the same way.

Hope this helps.

~Randal Schaffer