Enter one product. See the real contribution margin after freight, duties, marketplace fees, fulfilment, returns and ads — and the dollar gap between that and the number you're making decisions on.
One SKU. Use your average selling price after discounts and coupons.
What most sellers call "COGS" is only the first box. All four belong in landed cost.
Amazon referral fee on price, FBA fulfilment per unit, monthly storage spread per unit.
Returns cost you the fulfilment fee again plus whatever can't be resold. Ads are a per-unit cost, not "marketing".
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Most e-commerce P&Ls book the supplier invoice as cost of goods sold and everything else — freight, duties, marketplace fees, fulfilment, returns, ads — as operating expenses. Gross margin then looks healthy because half the real cost of selling a unit sits below the line. That is the number founders price against, reorder against and raise money against.
Landed cost = product cost + inbound freight + duty + packaging. Channel cost = referral or platform fee + fulfilment + storage + payment processing. Returns cost = return rate × (fulfilment fee again + unsellable share × landed cost). Advertising = TACoS × price. Contribution margin is price minus all four. It is the only per-unit number that tells you whether selling one more unit makes money.
Fixed costs — salaries, software, rent, your own time. Those come after contribution margin, and a product with a thin or negative contribution margin cannot carry them no matter how much volume you push through it. Defaults are typical for a $30–50 consumer product on Amazon US in 2026; replace every one of them with your own numbers.
We rebuilt exactly this for a $3.2M health & wellness brand and found a 23-point gap — $274K of profit that wasn't where the P&L said it was.
A margin review takes your actual Amazon and Shopify exports and rebuilds COGS per product, per channel. You get the real number, the gap, and what to do about it.