Margin vs markup: the same profit, two different bases

A product costs you $70 and you sell it for $100. Ask the buyer what the markup is and they will say 43%. Ask the accountant what the margin is and they will say 30%. Both numbers describe the same $30, and both are correct. The damage starts when someone prices a product, approves a discount or sets an ad target using one number while believing it is the other - and the error runs in the direction that costs money every single time.

This is not a vocabulary problem. It is an arithmetic problem with a predictable size: at a 30% margin the gap between the two figures is 13 percentage points, and at a 50% margin it is a full 50. Below are the formulas, a conversion table, and the three places where the confusion shows up on a P&L.

The two formulas differ only in the denominator

Margin = (Price − Cost) ÷ Price
Markup = (Price − Cost) ÷ Cost

Same numerator, different base. Margin asks what share of the selling price you keep. Markup asks how much you added on top of what you paid. Because price is always larger than cost, markup is always the bigger percentage, and it grows much faster: doubling the price gives you a 50% margin but a 100% markup.

The two convert cleanly in both directions, which is worth committing to memory because it removes the guessing:

Margin = Markup ÷ (1 + Markup)
Markup = Margin ÷ (1 − Margin)

So a 50% markup is a 33.3% margin. A 30% margin requires a 42.9% markup. If you would rather not do it by hand, the markup calculator and the profit margin calculator take cost and price and return both figures at once.

The conversion table worth pinning above your desk

Read the table once and the pattern is obvious: below roughly 20% the two numbers are close enough that sloppiness survives, and above 50% they diverge so far that any substitution is catastrophic. Traditional retail keystone pricing - doubling the wholesale cost - is a 100% markup and a 50% margin, which is exactly why the two words get used interchangeably in retail and almost nowhere else.

Error one: pricing to a margin target using markup

A finance team sets a 30% margin floor. Someone in purchasing implements it as “cost plus 30%”. On a $70 item that produces a $91 price, a $21 profit and a 23.1% margin - $9 per unit short of the instruction, and nobody notices because the spreadsheet column is labelled 30%.

The correct move is division, not multiplication. To hit a target margin, divide the cost by one minus that margin: $70 ÷ 0.70 = $100. On 4,000 units a quarter, the difference between $91 and $100 is $36,000 of gross profit that was never priced in. Nothing in the operation looks broken; the money simply never arrives.

Error two: discounting against the wrong base

Discounts are quoted off the selling price, so they eat margin at a rate most people underestimate. Take that $100 product at a 30% margin and run a 20% promotion. Price drops to $80, cost stays at $70, and profit per unit falls from $30 to $10 - a two-thirds cut from a one-fifth discount.

To hold total gross profit flat, that promotion has to triple unit volume. It rarely does. This is the arithmetic behind the familiar pattern where a strong sales week is followed by a weak P&L: revenue moved, contribution did not. Before approving any promotion, compute the breakeven volume lift rather than the headline discount, and if the answer is above about 1.5×, the discount is a customer-acquisition expense rather than a profit exercise - budget it as one.

Error three: feeding markup into an ad target

This is the version that shows up in paid media, and it is the most expensive of the three because the algorithm obeys whatever you tell it. Break-even ROAS is the reciprocal of contribution margin:

Break-even ROAS = 1 ÷ Contribution margin

Give it the true 30% margin and break-even sits at 3.33×. Give it the 43% markup by mistake and break-even appears to be 2.33×. An account running steadily at 2.6× then reads as comfortably profitable while it is in fact losing roughly $0.20 of contribution on every dollar of revenue, and the loss scales linearly with budget. Smart Bidding will happily buy more of it.

Contribution margin, not gross margin, is the input that belongs here: it deducts everything that moves with the order - cost of goods, shipping, payment processing, packaging and expected returns. On a typical ecommerce order those extras take another 8 to 15 points off the gross figure, which pushes real break-even ROAS well above what the merchandising team quotes. Work it out with the contribution margin calculator, then set the target with the break-even ROAS calculator rather than inheriting a round number from a previous agency.

Which one should you actually use

Use markup when you are setting a price from a cost you control - it is the operating instruction for a buyer or a production manager. Use margin everywhere a number gets compared, aggregated or reported: across products with different cost structures, against last year, against a competitor, or as an input to any acquisition maths. Margin is bounded at 100% and therefore comparable; markup is unbounded and is not.

One practical rule keeps the two apart in conversation: if the percentage is above 100, it is a markup, because no margin exceeds 100%. If someone quotes you a “60% margin” on a product they buy for $40, ask what they sell it for. At a 60% margin the answer is $100. At a 60% markup it is $64. That is a $36 discrepancy on a single unit, and it originates in one preposition.

A wider set of these definitions, including contribution margin, gross margin and AOV, sits in the finance and unit economics glossary.

The one thing to do today

Open the sheet where your product costs and prices live and add a single column: (Price − Cost) ÷ Price. Sort it ascending. Every SKU whose true margin is lower than the number your ad targets assume has been quietly buying customers at a loss, and you now have the list in front of you. Fix the targets on those first - it takes an afternoon and it does not require a single extra dollar of spend.

Benchmarks and conversion figures above are standard arithmetic, not promises about your category. Your cost structure decides the numbers; the formulas only decide whether you read them correctly.