Every experienced Amazon seller has a story about a product they thought would be profitable but was not. The difference between successful sellers and those who struggle is that successful sellers check the numbers before buying, every single time.
The Amazon FBA Revenue Calculator
Amazon provides a free FBA Revenue Calculator that every seller should bookmark. You can access it directly from Seller Central or by searching "Amazon FBA calculator" online. Enter the product's ASIN or search for it by name, and the calculator shows you the fee breakdown.
Input the selling price, your product cost, and the shipping cost to Amazon. The calculator shows the referral fee, fulfilment fee, and your estimated profit. It also lets you compare FBA versus FBM economics side by side.
What to Include in Your Cost Calculation
The Revenue Calculator gives you Amazon's fees, but your full cost includes several other items that you need to add manually. Your total cost per unit should include the purchase price, any shipping cost to get the product to you or your prep centre, prep centre fees (labelling, poly bagging, bubble wrap, etc.), and shipping to Amazon's fulfilment centre.
Many sellers forget to include prep costs and inbound shipping, which can add £0.50–£2.00 per unit depending on the product. Excluding these from your calculations means your real profit is lower than you expected.
The Quick Mental Maths Method
When you are scanning products in a shop or browsing online and need a quick estimate, use this rough formula. Take the Amazon selling price, subtract roughly one-third for Amazon's fees (this approximates the referral fee plus fulfilment fee for most standard-size products), then subtract your purchase price and an estimated £1 for prep and inbound shipping.
If the result is positive and represents at least 30% of your total investment (purchase price + prep + shipping), the product is worth investigating further with the full calculator.
The ROI Threshold
ROI (Return on Investment) is the most useful metric for evaluating Amazon products. Calculate it as: (Profit / Total Investment) x 100. If you spent £5 total on sourcing and prep and made £3 profit, your ROI is 60%.
Most experienced sellers target a minimum 30% ROI. Some target higher, especially for products that might sit for a while before selling. The reason for this threshold is that returns, price drops, and occasional slow sellers will eat into your average — starting with healthy margins gives you a buffer.
Checking Price Stability
A product might show great margins today, but if the price drops next week, your calculation is worthless. Always check the price history using Keepa before buying. You want to see that the selling price has been stable (or rising) over at least the past 90 days. If the price has been volatile, use the average price for your calculations rather than today's peak.
Factoring in Competition
Profitability is not just about today's numbers. If a product has five FBA sellers and you become the sixth, the existing sellers might lower their prices to compete, squeezing margins. If Amazon decides to start selling the product directly, prices could drop significantly. Consider the competitive landscape as part of your profitability assessment.
The Spreadsheet Habit
Successful sellers track their purchases in a spreadsheet — product name, ASIN, purchase price, expected selling price, estimated fees, expected profit, and actual profit once it sells. Over time, this data shows you which types of products and sourcing methods produce the best returns, and where you are consistently overestimating or underestimating margins.
Taking five minutes to check the numbers before buying saves you from weeks of watching a product sit unsold in Amazon's warehouse, accumulating storage fees. Make it non-negotiable — if the numbers do not work, move on.