Ecommerce math
See what FBA fulfillment + referral fees + ad spend do to your per-unit contribution. SKU-by-SKU margin math with a fee-hike sensitivity panel. Free. No signup.
Contribution per unit
$14.44
Standard healthy FBA contribution margin. Room to reinvest into ads, bundle testing, and inventory without cash-flow strain.
Ignores returns, storage fees, long-term storage surcharges, and removal fees. Deduct 3–6% for those on mature SKUs; 8–12% on apparel.
Ignores returns, long-term storage, inbound placement surcharges, and removal fees. Deduct 3–6% for those on mature SKUs and 8–12% on apparel before you sign an LOI.
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Seller Central → Manage FBA Inventory → the SKU detail page surfaces the current fulfillment fee based on weight + dimensions. It updates as Amazon reclassifies tiers. If you're diligencing a deal, ask the seller for a 12-month fee audit — FBA fees change and small-standard may drift into large-standard with a SKU size change.
ACoS is ad spend ÷ ad-driven revenue (how efficient your ads are). TACoS is ad spend ÷ total revenue (how dependent the SKU is on ads). This calculator uses TACoS because it's what actually hits the P&L: if TACoS is 15% you need 15% margin buffer to scale ads without going unprofitable.
Gross margin ignores the variable costs that matter most on Amazon — fulfillment, referral, and ads — and brands routinely look "55% gross margin" but end up with a 12% contribution margin once those hit. Contribution margin is the number that funds operating expenses, growth, and eventual owner take-home.
Three to diligence: (1) annual inbound placement and long-term storage surcharges, especially for slow-moving apparel/beauty; (2) size-tier reclassification — a redesigned box can bump a SKU into a higher fulfillment tier overnight; (3) category referral-rate changes, which Amazon reserves the right to adjust. This calc's sensitivity panel shows a +10% FBA fee hit — treat it as a floor for annual fee-related risk.
Not modeled here. Typical Amazon return rates: 3–6% consumer goods, 6–10% electronics, 10–30% apparel/beauty. Multiply the contribution by (1 − return rate) to get a more honest number, and remember Amazon keeps the referral fee on most returns.