How the calculation works
Selling price = cost ÷ (1 − target margin ÷ 100).
A worked example
A cost of 80 at a 20% target margin needs a selling price of 100. Adding 20% to cost would give only 96.
Use the result carefully
Margins must be below 100%. This is a gross-margin calculation for a single price, not a forecast of take-home income.