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How This Tool Works
Calculation Method
Computes Net profit per unit from Selling price, Product cost, Shipping to Amazon, Referral fee, FBA fulfillment fee, Monthly storage and Units sold per month.
Site methodology
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Assumptions to Verify
- Marketplace and payment fees are user-entered estimates.
- Returns, taxes, advertising, and overhead may require separate allowances.
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Where a $29.99 sale goes
What this means for your numbers: At the worked example's $29.99 price, fees consume 34% of revenue. Every $1 of price increase falls through to net at 85 cents (referral is the only percentage fee), while a $1 sourcing saving falls through 100%.
Illustrative breakdown using the worked example above. The calculator computes your own numbers with the same formula.
Worked example: $25 product, 100 units a month
Take a product selling at $25.00. Your unit cost is $8.00, inbound shipping to the warehouse adds $2.00 per unit, Amazon fulfillment is $4.25 (a mid-size standard tier), monthly storage is $0.50, and you sell 100 units a month at the default 15% referral rate.
The referral fee is 15% of price: 25.00 x 0.15 = $3.75. Total fees are 3.75 + 4.25 + 0.50 + 2.00 = $10.50 per unit. Net profit is 25.00 - 8.00 - 10.50 = $6.50 per unit, which is a 26.0% margin (6.50 / 25.00 = 0.26). At 100 units, monthly profit is 6.50 x 100 = $650.00.
The breakeven formula answers a different question: what is the lowest price at which profit hits zero? It is (cost + ship + fulfillment + storage) / (1 - referral rate) = 14.75 / 0.85 = $17.35. The division is needed because the referral fee is charged on the selling price itself, so the fee shrinks as the price falls. At $17.35 the referral fee is 17.35 x 0.15 = $2.60, and 14.75 + 2.60 = 17.35, which confirms the answer closes exactly. If you shipped the same product with a 10% referral rate, breakeven would be 14.75 / 0.90 = $16.39 instead. That $0.96 spread per unit is why category rate changes matter even when nothing else moves.
Where this calculator stops being exact
The formula treats fees as straight lines, and Amazon's real fee schedule is not one. Referral is 0% below the threshold in promotional categories (a $10.00 sale there keeps every dollar of the 3.75 that the default rate would charge, moving breakeven from $17.35 down to $14.75), and it steps by category between 8% and 15% at boundaries that are hard cutoffs, not percentages. A product priced $1 over a tier boundary loses a larger slice of that dollar than one priced $1 under it.
Storage is charged per cubic foot and jumps in October through December, when the monthly rate rises by roughly 2 to 3x, so the flat $0.50 field understates Q4 cost for any bulky item. Fulfillment also depends on size tier and dimensional weight: a $4.25 estimate for a product that Amazon tiers up one weight band is easily $2.00 too low, which at the worked example's 100 units is $200 a month of phantom profit. Long-term storage surcharges (about $6.90 per cubic foot at the 271-day mark) never appear at all.
Zero and negative inputs behave predictably but not helpfully. Set units to 0 and monthly profit shows $0.00 even though per-unit economics are fine; set selling price to 0 or less and the tool refuses to compute rather than showing a $0 unit. Storage or shipping of 0 is legitimate (merchant-fulfilled, zero-fee categories) but silently hides the surcharges above. FBA New Selection and brand-tailored rebates can also change real fulfillment rates versus the published tier table, so the result-note warning to verify against Seller Central is the part that actually protects the margin math.