What is markup?
Markup is how much you add on top of the purchase price, as a percentage of that price.
Markup and margin are often confused. A 100 % markup is a 50 % margin.
For ad calculations use margin, not markup, otherwise break-even will look better than it is.
Formula
Markup = (price - cost) / cost x 100
Example
You buy for 40 EUR and sell for 60 EUR. Markup is 50 %, margin is 33 %.