The simple formula, and why it is hard in practice
True net profit per unit is straightforward on paper: selling price − product cost − Amazon fees − ad spend per unit. The difficulty is that the deductions are scattered across different reports and change over time. A back-of-envelope "price minus cost" almost always overstates profit because it skips the fees Amazon takes and the advertising that drove the sale. You can sanity-check a single product on the Amazon profit calculator.
The costs sellers forget most
Four deductions do the most quiet damage:
- Referral + FBA fees — together often 25–40% of the selling price, the biggest bite after product cost.
- Returns and refunds — a returned unit costs you the refunded sale, return shipping, and sometimes unsellable stock. Spread across all sales, a high return rate can erase a thin margin.
- Advertising — ad spend never shows on your Amazon payout, so it is the easiest cost to ignore, yet it is a real per-sale expense.
- Storage and the long tail — monthly and long-term storage fees, prep and aged inventory drain margin on slow movers.
Attributing ad spend per unit
The trickiest piece is advertising, because it is not charged per order on your statement. A workable approach: take a campaign's spend over a period and divide by the units it sold to get an ad cost per unit, then subtract that from each sale's margin. It is an approximation, but ignoring ad spend entirely is the bigger error. If you want to see where advertising starts eating your margin, the break-even ACoS calculator shows the ACoS at which an advertised sale breaks even.
Why per-SKU beats a single blended number
A blended account-wide margin hides the products that are losing money behind the ones that are winning. The real insight comes from profit per SKU: it tells you which products to push, which to reprice, and which to stop advertising. A single healthy-looking total can mask several quietly unprofitable SKUs.
Keeping it current without a spreadsheet
Doing this once by hand is useful for a decision; keeping it current for a whole catalogue, as fees and returns shift, is a different job. That is what profit reports in AIAdKing automate — pulling your fees, costs and settlement data to compute true profit per SKU continuously, reconciling settlements and flagging loss-making SKUs. However you do it, the discipline is the same: count every cost, every time, and trust the number that remains.