Free calculator
What a promotion does to one unit's contribution, with VAT and the payment fee rescaled on the discounted price, and the volume the code must bring in before the month has merely stood still.
Extra orders needed to stand still
+35,6%
Sticker discount
€4,90
what the customer sees
25Contribution given up
€4,03
per unit; VAT and fee absorb the rest
25Contribution after
€11,32
was €15,35
The shelf price. VAT is stripped before any contribution is computed, because it was never your money.
What one order adds
The parcel and the payment fee exist because the sale happened, and both belong in the before-and-after: the fee even moves with the price.
↑ ↓ to nudge, Shift for ten. Commas or dots both work.
Before running the code, ask one honest question: has any promotion on this product ever lifted its volume by that much? If not, the discount is a plan to earn less.
The promotion takes €4,03 of contribution out of every unit, so it has to sell 35,6% more units just to keep the month's total contribution level.
An estimate from flat rates. In nouz every order is priced from the costs of its own day.
A discount impact calculator works out what a price discount does to one unit's contribution and how much extra volume the promotion needs just to stand still. VAT is stripped and the payment fee rescaled on the discounted gross, so the answer is what a P&L would see, not what the sticker says.
The formula
A discount is judged against revenue and paid out of contribution, and that mismatch is the whole story. The goods, the parcel and the fixed part of the payment fee cost exactly the same on a discounted order, so every cent the code gives away comes out of the thin slice the unit was actually keeping.
That is why the required volume lift is always steeper than intuition expects. When roughly a third of the net price survives the variable costs, ten percent off the price is about a quarter off the contribution, and the promotion has to sell more than a third more units before the month has gained anything at all.
The per-unit cost, on the other hand, is slightly kinder than the sticker: the VAT inside the discounted part was never yours, and the gateway’s percentage shrinks with the price. Both effects are in the calculator, because both are in a real statement.
Where it goes wrong
Every one of these makes a code look better than it was, which is why discount habits grow until a statement stops them.
A promotion that lifts revenue can easily shrink contribution: the extra orders arrive, each carrying a quarter less margin, and the month ends busier and poorer. The only honest benchmark is total contribution against the un-discounted baseline, which is exactly the volume ratio this calculator leads with.
The required lift is arithmetic; the actual lift is an experiment. Before a code runs, write down the volume it owes you. Afterwards, compare. Most stores that do this once discover their standard promotion has never paid for itself, and their best one earns quietly at half the depth.
The fixed costs of an order, parcel and the fixed leg of the payment fee, do not shrink with the price, so a deep discount on a small basket can push the whole unit under water. A promotion that sells below contribution is not marketing; it is paying customers to take stock away.
A sitewide code gives its discount to every full-price customer already in the checkout, and that share of the spend buys no lift at all. Scoping promotions, to slow stock, to first orders, to a category, is the cheapest way to shrink the giveaway without shrinking the effect.
Worked example
The calculator’s own defaults: a product on the shelf at €49,00 including 19% VAT, bought in for €18,50, shipped for €6,40 all-in, paid through a gateway taking 1,9% of the gross. Before any code it contributes €15,35 per unit.
The 10% code moves the sticker to €44,10. The net price falls to €37,06, the fee eases to €0,84, and the contribution lands at €11,32.
The €4,90 sticker discount cost €4,03 of contribution, and that €4,03 came out of €15,35: a 26% cut in what the unit keeps, from a 10% cut in what it charges. To hold the month’s total contribution level, the promotion has to sell about 35,6% more units, and only the orders beyond that line earned anything.
The same leverage runs the other way, which is what the price increase calculator below is for.
In the app
A calculator works from flat rates you type once. nouz prices every single order from the cost rules that were in force on that order's own date, and rebuilds the same statement every night from your own orders and your own ad spend.
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Each one is a different question about the same statement. All 32 are free, and none of them asks you to sign up.
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The long version
Want the long version rather than the arithmetic?
CM1 · CM2 · CM360,8% · 48,9% · 23,5%the same revenue, three margins10 min readCM1, CM2 and CM3 explained: the three margins ecommerce operators steer onCM1, CM2 and CM3 are contribution margins after product, fulfilment and marketing costs. What each level includes, the formulas, and a worked example.CM1, CM2 and CM3 explainednouz books every discount to its own P&L line, per day and per product, so a promotion is judged by what the month kept rather than by what the code sold.