Calculating selling price from the cost price

Recently in my price matching system I had to calculate the selling price of a product in a way that also calculates a transaction fee percentage on the final selling price without knowing the selling price, and without knowing what the transaction fee is until you’ve calculated the total price. Had fun chasing your tail yet?

You can do this in Excel with circular references but you will get circular reference warnings and the only way is to allow these warnings and an iteration limit of 100.

Stepping aside from the magic of excel I was able to work out the exact formula for this and below is a calculation for anyone else struggling to work out how to do this.

$cp = 9.56; // cost price
$d = 2.50; // delivery fee
$m = 0.15; // margin 15%
$tf = 0.019; // transaction fee

$sellingPrice = (($cp+$d)*(1+($m)))/(1-((1/6)+$tf)*(1+($m)));

$costPrice = $x / (1+(.15));

echo $sellingPrice."\n";
echo $costPrice;