The most basic formula in retail is Cost + Mark Up = Selling Price. “Cost” is the amount you pay for an item and “mark-up” is the amount by which retailers increase the price to cover expenses and profit. Under the retail method, the selling price of an item is always 100%. Both costs and mark up can be expressed as a percentage of the “selling price”. Keep in mind cost nor mark up can ever be more than 100%. If for example, you bought an item for $48.00 and sold it for $100.00 your gross profit or margin would be $52 and your mark up would be 52%. Every retailer in the world should know their costs, mark up, and selling price.