Discount Price Calculator

Setting it out

Discounted price is the original times one minus the discount: price × (1 − discount). The saving is price × discount. Both are trivial arithmetic, and the number that matters is neither of them.

The number that matters is the volume increase required to hold contribution: margin ÷ (margin − discount). At a 50% margin a 20% discount needs 1.67 times the units. At 30% margin the same discount needs 3 times.

Worked through

A $58 product with a 55% margin, discounted 20%. The new price is $46.40 and the saving is $11.60.

The margin falls from 55% to 43.75%, because the cost of $26.10 is now a larger share of a smaller price. Contribution per unit drops from $31.90 to $20.30, a 36% reduction from a 20% discount.

To hold total contribution, unit sales have to rise by 57%. Not 20%. If the promotion produces a 30% uplift, which would feel like a success on any dashboard, contribution falls by 17%.

Where it goes wrong

Revenue rises long before contribution does, which means a discount can look successful on every metric a business commonly watches while destroying profit. A 30% volume uplift on a 20% discount raises revenue by 4% and lowers contribution by 17%.

The discount also reaches customers who would have paid full price, and on an established product that is most of them. The incremental cost per genuinely new sale is far higher than the discount percentage suggests.

Making it useful

Calculate the required uplift before setting the discount, and compare it against what previous promotions actually delivered. If a 20% discount needs a 57% uplift and your best promotion ever produced 40%, the arithmetic has answered the question.

Where a discount is unavoidable: clearing stock, matching a competitor, a category-wide event, prefer mechanisms that require something in return. A threshold, a bundle or a multi-buy gets the volume the discount is paying for, where a straight percentage off does not.

The required-uplift table worth keeping

At a 60% margin: a 10% discount needs 20% more units, 20% needs 50%, 30% needs 100%. At 50% margin: 10% needs 25%, 20% needs 67%, 30% needs 150%. At 40% margin: 10% needs 33%, 20% needs 100%, 30% needs 300%.

Two patterns fall out. The required uplift rises far faster than the discount, and it rises faster still as margin falls, which means the businesses least able to afford a discount are the ones for which it is most expensive.

The practical use is as a veto. Pinning the table to the wall where promotions are planned turns a conversation about how much to discount into a conversation about how much volume anyone genuinely expects, and the second conversation is far shorter.

It is worth setting a hard floor in the platform rather than relying on judgement. Discount codes stacking with sale prices is the most common route to selling below cost, and it happens at exactly the busy moments when nobody is checking.

The floor should be calculated per product from the actual variable cost, not set as a single sitewide percentage. A uniform floor is either too permissive on low-margin lines or too restrictive on high-margin ones, and usually both at once.