This creates a circular reference.

"TomPl" wrote:

Put your formula in P13.
Change the formula to =B13-SUM(C13:O13)
Column O will remain blank.
Add new column before column O and the new column will automatically be
included in the formula.
You cannot hide column O because then you will not be able to add a column
before it.
Make Column O real narrow to separate the data from the formula and to
remind you to insert columns before it.

Tom