- Contribution per unit = price − listed reference fees − your entered per-unit costs.
- Contribution margin puts that remainder over price; ROI puts it over goods cost + inbound shipping.
- When goods and inbound are both zero, ROI has no basis and is withheld — not shown as 0% or infinity.
- The numbers come from one fixed US reference profile, not a general Amazon fee quote.
On this page
One sold unit leaves a specific amount of cash behind. This guide walks the three numbers the calculator prints from that single ledger, on the same fixed reference profile the tool computes with.
What contribution subtracts
Contribution starts from your selling price and subtracts two groups. Amazon’s listed reference fees for this profile: a referral fee of 15% of the price (rounded to 2 decimals), $3.63 FBA fulfillment ($3.51 base plus a $0.12 fuel surcharge), the $0.30 default placement reference, and peak storage of $0.01666 per unit-month, allocated as average inventory divided by units sold. Then your entered per-unit business costs: goods, inbound shipping to Amazon, advertising, a returns allowance, and anything else. What remains is contribution per unit — money that still has to cover overhead, tax and actual profit. It is deliberately not full business net profit.
Margin and ROI answer different questions
Contribution margin divides contribution by price: how much of each sales dollar survives the ledger. ROI divides the same contribution by the cash you sink per unit — goods cost plus inbound shipping — and multiplies by 100: how hard the money you stock works. The two can rank products differently. Expensive goods against a high price can mean strong margin but weak ROI; cheap goods on a modest price can show the reverse.
When ROI is withheld
If goods and inbound shipping are both zero, ROI would divide by nothing. The calculator withholds it rather than printing a misleading 0% or an infinity sign; contribution and margin still appear, and the blank ROI is the honest answer: no cash basis yet.
Scope and sources
These definitions belong to the fixed US reference profile — Home and Kitchen, 6 × 4 × 0.5 in, 2 oz, prices $10–$50, default reference placement — with fees observed on 2026-11-06 and a review cutoff of 2026-11-30, unchanged since. The full data and limitations: fee reference data. Official sources: Amazon revenue calculator, selling plans and pricing, and the 2026 fulfillment fee reference. Run your own numbers in the FBA Unit Profit Calculator.