What does it mean?
Markup measures the difference between selling price and cost as a percentage of cost. Margin measures that same difference as a percentage of selling price. The denominator changes, so the percentages are not interchangeable. Confusing them can reduce the return on a job even when all measured quantities and supplier prices are correct.
In practice
On a cost of 1,000, a 20% markup gives a price of 1,200 and a margin of 16.67%. To achieve a 20% margin, divide 1,000 by 0.8 to obtain a price of 1,250.
Keep in mind
For a useful comparison, record the currency, pricing date, scope and exclusions alongside the amount. Separate measured quantities from unit prices so you can identify whether a change comes from design or pricing. Use project-specific quotations where available, and distinguish an illustrative allowance from a confirmed cost. The calculators show arithmetic relationships; they do not supply current market rates, tax advice or a complete project budget.