Sales mark-up is the difference between the selling price of a good or service and its cost. The selling price includes the markup, which is the amount that the seller adds to the cost to cover his or her expenses and profit. To calculate sales markup, simply take the selling price and subtract the cost. Sales markups are often used in retail settings, where businesses need to cover their overhead costs and make a profit. Many times, businesses will have different markups for different products, depending on how much they cost to produce or acquire.