How this instrument works
A discount is subtracted from what the customer pays, but the cost of the item never moves — so every dollar of markdown comes directly out of what would otherwise have been profit, not out of the cost base underneath it. That is why the erosion in margin is always steeper, proportionally, than the discount rate itself: a 15% price cut on a 40%-margin item does not shave 15% off the margin, it removes over a quarter of it, because the whole discount is drawn from the thinner profit slice rather than spread across the full price.
There is an exact threshold buried in the formula: the discount percentage that drags margin all the way down to zero is numerically identical to the original margin percentage at list price. An item priced to carry a 40% margin can absorb discounts up to, but never past, 40% before the discounted selling price meets the cost — one point beyond that line and every unit sold moves the business backward instead of forward.
Retail buyers and e-commerce merchandisers reach for this relationship before a promotion goes live, because the price tag and the margin line tell two different stories about the same markdown. A '15% off' banner reads as a modest concession to a shopper; the same banner reads, on the margin line, as a much larger bite out of the money the sale was supposed to leave behind, which is why discount depth gets modeled against margin and not against the sticker price alone.
- Enter what the item cost you into Cost, $ — the figure the discount never touches.
- Enter the full sticker figure into List price, $ before any promotion is applied.
- Set Discount offered, % to the markdown you are planning, such as 15 for a 15%-off sale.
- Read Discounted selling price for the amount the customer actually pays.
- Read Margin after the discount, % to see how much profit share survives the sale.
Worked example — the $100 item at 15% off
Take an item that costs $60 and lists at $100 — a 40% margin before any promotion runs. Offer 15% off and the discounted selling price is 100 × (1 − 15 ⁄ 100) = $85.00, exactly $15.00 below the ticket.
Margin after that sale is (85.00 − 60) ⁄ 85.00 × 100 = 29.4117647059%, which this sheet displays as 29.41%. Margin fell from 40% to 29.41% — a relative drop of about 26.5%, noticeably steeper than the 15% taken off the price — because the entire $15.00 markdown came out of the $40.00 that was profit at list price, none of it out of the $60.00 cost underneath.
Questions
Why does a 15% discount take more than 15% off my margin?
Because the discount is subtracted from the price, not spread across cost and profit — every dollar it removes comes out of the profit slice alone. On the $100/$60 example here, a 15% markdown drops margin from 40% to 29.41%, a relative fall of about 26.5%, noticeably steeper than the 15% headline discount. The thinner the starting margin, the sharper that gap gets.
What discount would wipe out the margin completely?
Exactly the original margin percentage, no more and no less. An item priced to carry a 40% margin reaches a selling price equal to its cost at a 40% discount — set Discount offered, % to 40 on this sheet and Margin after the discount, % returns zero. Push the markdown past that line and the item sells below cost, turning every unit into a loss rather than a smaller profit.
Does subtracting the discount from the margin give the right answer?
No — margin and discount are measured against different bases, so they cannot be subtracted directly. Discount is a share of the list price; margin is a share of the discounted price. Forty percent margin minus a 15% discount is not 25%; the true figure here is 29.41%, because the denominator itself shrinks along with the numerator once the markdown is applied.
Why does cost never appear to move in this calculation?
Because a discount is a pricing decision, not a purchasing one — what you paid your supplier is fixed before the sale is ever announced. The markdown only ever acts on the gap between list price and cost, which is why the whole reduction lands on profit. If the cost itself changes, that is a separate negotiation this sheet does not model.
Is clearance pricing the same arithmetic as a regular sale?
Yes, just pushed further along the same line. A clearance rail moves Discount offered, % close to the original margin percentage, so Margin after the discount, % approaches zero. Beyond that point the item is sold below cost, which some clearance strategies do on purpose to move stock, at the price of a loss on each unit sold.
Does a thinner starting margin make discounting more dangerous?
Yes. A 10%-margin item can only absorb a 10% discount before it sells at cost, while a 50%-margin item can absorb up to 50%. The same 15% markdown that costs a 40%-margin item roughly a quarter of its margin can wipe out most or all of the margin on a thin-margin item, which is why low-margin categories get discounted more cautiously.
References
- U.S. Small Business Administration — pricing guidance for small firms
- FTC — Guides Against Deceptive Pricing, 16 CFR Part 233
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.