How the Amazon FBA profit calculation works
Each unit sold earns net revenue (the price, less output VAT if you're registered). From that we take your landed product cost, inbound shipping to Amazon's warehouses, prep, the referral fee (a percentage of the price the customer pays), the FBA fulfilment fee you enter, any other per-unit fees and a returns allowance. That's profit before ads; subtract ad spend per order for profit after ads. Monthly costs — the Professional subscription, storage and your overheads — come off the monthly total.
We deliberately don't estimate the FBA fee. It depends on size tier, weight, dimensions, category and surcharges, and Amazon has changed fees during 2026. Use Amazon's own Revenue Calculator for your exact ASIN and copy the number in.
Worked example: £24.99, VAT registered, Professional plan
With the example values: the customer pays £24.99, of which £4.16 is output VAT, leaving £20.83 net revenue. The illustrative 15% referral fee is £3.75 (on the full price paid), and the example FBA fee is £3.20. After £6 landed cost, £0.40 inbound, £0.30 prep and £0.50 returns, profit before ads is £6.68. With £2.50 ads it's £4.18 per unit — 20.1% of net revenue and 62.3% ROI on product cost. At 150 units, minus the £25 Professional fee and £15 storage, that's £586.48 a month.
Individual vs Professional plan
Individual charges a per-item fee on every unit sold (example £0.75 ex VAT), so it sits in per-unit costs. Professional is a flat monthly subscription (example £25 ex VAT), so it sits in monthly fixed costs. In this example, Individual would give £498.98 a month against £586.48 on Professional — at higher volumes Professional usually wins, but check what each plan includes, not just price.
Amazon quotes these fees excluding VAT. If you're VAT registered and reclaim VAT on fees, leave "irrecoverable VAT on fees" at 0. If you aren't, enter 20 so VAT on referral, FBA and plan fees is counted as a cost.
Common mistakes
- Calculating the referral fee on the ex-VAT price — it's based on the total price the customer pays.
- Guessing the FBA fee from category; use the size and weight-based fee for your product.
- Forgetting inbound shipping, prep and long-term storage.
- Comparing campaign ACoS with break-even ACoS on different bases. Amazon's ACoS uses gross ad-attributed sales (VAT included), so break-even ACoS here is break-even CPA ÷ the gross price paid. It excludes monthly costs such as the plan fee, storage and overhead — target lower to cover them.
- Judging ads by ROAS alone without comparing it to your break-even ROAS.
- Ignoring referral fee minimums, which can matter for low-priced items.