In plain English
Markup starts from cost. If a unit cost you $100 and you sell it for $150, you added $50 to a $100 cost, so the markup is 50%.
Markup is a pricing tool. It is how you decide what to put on the tag. It is not how you measure how much of that sale you kept, that is margin.
Example
Cost $100, price $150. Markup = $50 ÷ $100 = 50%. Margin on the same sale = $50 ÷ $150 = 33%.
Why it matters
Most resale pricing is built on a markup rule of thumb. If your rule is set against the wrong cost number, every ticket in the building is wrong by the same amount.
COMMON MISTAKEMarking up the invoice price and forgetting freight, fuel, repair parts and the loads that never sold. Mark up landed cost, not invoice cost.