How to calculate betting exchange commission into odds

I have a spreadsheet I made up for layig the draw then trading out by backing the draw .
But i cant work out how to ADD COMMISSION INT MY FORMULA.
Any excell formula you can forward to me as an examl
ple.Robert

Blockquote

Not sure exactly what you mean, but my spreadsheet has the following…
I have spreadsheets for numerous different trading/arbing combinations.
Contact me if you still need help
mikepcon@gmail.com