A markup is what percentage of the cost price do you add on to get the selling price.
Markup is the difference between the cost of a good or service and its selling price. A markup is added on to the total cost incurred by the producer of a good or service in order to create a profit. The total cost reflects the total amount of both fixed and variable expenses to produce and distribute a product. Markup can be expressed as a fixed amount or as a percentage of the total cost or selling price.
Markup is is calculated against Cost
Markup –The amount added to estimate line items (or the percentage figure items are multiplied by-JJH) to cover payroll on-costs, supervision, administration and profit. Alternatively may just refer to the overhead and profit added to the bottom of an estimate for purposes of submitting a bid or invoice.
(Wideman Comparative Glossary of Common Project Management Terms v2.1)
Markup – Markup, defined as the percentage added to cost to arrive at a selling price, is commonly used to price materials. If you want to mark up an item 20%, you add 20% of the item’s cost to the cost.