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
Other Definitions
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.
(Wickes.com LumberYardMath)