Calculate Percentage Markup is an official business term that describes the method of adding a predetermined percent increase to a base price. This percentage increase can be anything from a 5% mark-up to a 20% mark-up, depending on the item. It is used by retailers and wholesalers to make sure they are making a profit while selling their goods at a competitive price. By calculating percentage markup, businesses can accurately determine how much it costs to produce something and how profitable items will be if they sell them.