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How Discounts Eat Margin Calculator

A 20% discount doesn’t cost you 20% of your profit — it costs far more. Enter your price, unit cost, and discount to see the margin that survives the sale, how many margin points the discount eats, and the deepest discount you can offer without losing money.

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How much margin survives your discount

Enter the price, your unit cost, and the discount — the calculator shows the margin before and after, the margin points the discount eats, the deepest discount that still makes money, and the discount that would halve your margin. Optionally set a minimum acceptable margin and it solves for the deepest discount you can offer.

How it works: margin = (price − cost) ÷ price × 100 — the denominator is the price, not the cost. Sale price = price × (1 − discount ÷ 100), and the after-discount margin uses the sale price on top and bottom. On load with the defaults ($100 price, $60 cost, 20% discount): sale $80.00, margin after discount 25.0%, 15.0 margin points lost, and 40.0% is the deepest discount that stays profitable. Nothing you type leaves your device.

What a discount does to your margin

Margin is the share of the selling price you keep: (price − cost) ÷ price × 100. The painful part is that a discount attacks both halves of that fraction at once — it shrinks the profit dollars on top and the sale price on the bottom. That is why a 20% discount on a $100 item costing $60 doesn’t trim 20% off your profit: profit falls from $40 to $20 (half the dollars) while margin falls from 40% to 25% (15 full margin points).

Output · formula · meaning

Output	Formula	What it means
Sale price	price × (1 − discount ÷ 100)	What the customer pays: $80.00 on the defaults.
Margin before discount	(price − cost) ÷ price × 100	Your starting margin — 40.0% on the defaults ($40 profit).
Margin after discount	(sale − cost) ÷ sale × 100	The margin that actually lands in your pocket — 25.0% on the defaults ($20 profit).
Margin points lost	margin before − margin after	The discount’s true cost in margin points — 15.0 here, not 20.
Max discount to stay profitable	(price − cost) ÷ price × 100	The deepest discount that keeps profit at zero or above — 40.0% on the defaults, the same number as your starting margin.
Discount that halves margin	solve (sale − cost) ÷ sale = margin ÷ 2	25.0% on the defaults — half your margin is gone well before you reach the max discount.

Worked example: the 20% sale that eats half the profit

You sell a product for $100 that costs you $60. Margin before any discount: ($100 − $60) ÷ $100 = 40.0%, or $40 per unit. Run a 20% sale: the sale price is $100 × (1 − 0.20) = $80, profit drops to $80 − $60 = $20, and margin becomes $20 ÷ $80 = 25.0%. The discount cost you 15.0 margin points and half your profit dollars — even though it was “only” 20% off. Set a 10% minimum acceptable margin and the calculator finds the deepest discount you can offer: 33.3%.

Who uses this

Pricing managers: testing promo calendars — how deep can the holiday discount go before margins break the plan.
E-commerce sellers: checking that a marketplace “sale price” still leaves room after fees and shipping are accounted for.
Sales reps: knowing their walk-away discount on a deal without calling finance first.
Business students: seeing, in real numbers, why a discount costs far more than its face value.

Accuracy & limitations

This is gross margin on unit economics only — it does not include shipping, payment-processing fees, returns, ad spend, or taxes, all of which push real margins lower. It assumes one unit and a single discount; stacked promotions compound rather than add (20% then 20% is 36% off, not 40%). Percentages round to one decimal place. This page does arithmetic, not pricing advice — validate discount strategy against your full cost picture.

Compare with the plain sale-price math in the discount calculator, see how margin and markup translate in the profit margin calculator, model stacked promos with the stacked discounts calculator, and get the full method in the how to calculate margin guide.

Cite this calculatorBright Side Kit. “How Discounts Eat Margin Calculator.” brightoolbox.com, 2026.

Bright Side Kit. "How Discounts Eat Margin Calculator." https://brightoolbox.com/margin-discount-calculator/ Accessed October 21, 2026.

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Frequently asked questions

What’s a good profit margin?

For gross margin, anything above 20% is healthy for most small businesses; 5–20% is workable but tight, and under 5% leaves almost no room for error. What counts as “good” varies by industry — services often run 60%+, retail 30–50%, grocery 20–30% — so compare against your own category, not an internet average.

Does a 20% discount really cut my profit by 20%?

No — it cuts it by far more. On a $100 item costing $60, a 20% discount takes profit from $40 to $20: a 50% cut in profit dollars, and margin falls from 40% to 25% (15 margin points). The discount shrinks both the profit and the sale price, which is why discounts feel mild and land brutal.

Margin vs markup — what’s the difference?

Margin divides profit by the price; markup divides profit by the cost. On $60 cost / $100 price: margin = ($100 − $60) ÷ $100 = 40%, markup = ($100 − $60) ÷ $60 = 66.7%. Same transaction, two different numbers — using the wrong one overstates what you keep.

How do I find the deepest discount I can offer?

Set your minimum acceptable margin in the calculator and it solves for the deepest discount that keeps margin above it. Without a floor, the deepest discount that keeps profit at zero is exactly your starting margin — 40% off on a 40% margin item breaks even (before overhead).

What discount cuts my margin in half?

Solve (sale − cost) ÷ sale = margin ÷ 2. On the $100/$60 example it’s 25% — noticeably less than the 40% that would wipe the margin out entirely. The calculator computes it for any price and cost.

Should I calculate margin before or after the discount?

After. The before-discount margin is your pricing; the after-discount margin is your reality — it’s the number that actually hits your books. Always judge a promotion by the margin that survives it, not the margin you started with.