Markup is the increase over cost, expressed as a percent of cost (price = cost × (1 + markup%)). Margin is profit expressed as a percent of the sale price (margin% = profit ÷ price). The same dollar profit gives a higher markup % than margin % — mixing them up is a common pricing mistake.
Because each percentage applies to a different base. $100 minus 50% is $50; $50 plus 50% is $75, not $100 — percent changes aren't symmetric once the base number has changed.
If a rate moves from 10% to 15%, that's a 5 percentage-point increase, but a 50% relative increase (5 is 50% of 10). Both are correct — they're just answering different questions — but reports often blur this distinction.