You can calculate the percentages on the worksheet, and use a formula to
create the labels. For example, with the following data in in A1:B3 --
Jan 25
Feb 25
Mar 50
Enter the following formula in cell C1, and copy down to C3:
=B1/SUM($B$1:$B$3)
To calculate the text for the pie chart labels, enter the following
formula in cell D1, and copy down to D3:
=B1 & " " & TEXT(C1,"0%")
When you create the pie chart, in step 2 of the Chart Wizard, click on
the Series tab. Click in the Category Labels box, and then select cells
D1
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3 on the worksheet.
In step 3, choose Show Label on the Data Labels tab.