Having a little trouble, so let me give you more info.

my data table has the domain portion of the email address in Column A and
the extension portion of the email address in Column B.  So A2 might read
john@school and B2 might read "com" for example.  All the usernam@domain
portions of the email address are in Column A and all the extensions are in
Column B (.com, .org, .gov, .net, etc.)

My pivot table selects just Column B from the data table.  Then I drag the
column title (extension) to the "drop row fields here" section of the pivot
table and I also drag it to the "drop data items here" portion of the pivot
table.  The result is a list of all the extensions and a count of each one
with a total at the bottom.

Now I want to calculate the percentage of the total for each extension type
so that the row might read: "com > 147 > 72%"

In the cell next to the count of the "com" I put "=B5/B11" and it produces
the correct result even though the formula that actually that appears looks
like this:  =GETPIVOTDATA("ext",$A$3,"ext","com")/GETPIVOTDATA("ext",$A$3)

I cannot seem to copy this formula down so that all the different email
extensions count will show an equivalent percentage of the total.  I guess I
do not understand the dialog box that appears when I try to Insert
Calculated Item.