How to Calculate Your Real Profit Margin on Amazon (FBA & FBM)

The revenue you see in your Amazon dashboard is not the money that ends up in your pocket. What is left after commission, shipping, advertising, returns and currency differences are deducted from the sale price — your net profit — is usually smaller than you expect. In this guide we calculate a product’s real profit margin step by step, with example numbers.

Margin and ROI: two different questions

These two metrics are often mixed up, but they answer different questions:

• Profit margin = Net profit ÷ Sale price. It answers “out of every 100 dollars I sell, how much do I keep?”
• ROI (return on investment) = Net profit ÷ Money tied up in the product. It answers “how many dollars does each 100 dollars I invest bring back?” — the critical metric for arbitrage sellers in particular.

A low-margin product that turns over quickly can produce better ROI than a high-margin product that sells slowly. You need to track both together.

The cost items you must account for

• Product cost (COGS): What you pay to source the product, plus any cost of getting it to you (intermediate shipping, prep).
• Amazon referral fee: A percentage of the sale price that varies by category. See the referral fee guide for details.
• Logistics: Fulfillment and storage fees if you use FBA; your own shipping and packaging costs on FBM. For a comparison, see the FBA/FBM guide.
• Advertising (PPC): Ad spend allocated per product. Dividing total ad spend by total sales gives you a rough average share per unit.
• Returns: A share of sales equal to your return rate comes back — plus return processing and the cost of units that can’t be resold.
• Currency: If you earn dollars or pounds but your costs are in lira (or the reverse), which exchange rate the math uses moves the margin significantly.

A step-by-step worked example

The real picture for a product selling at $49.90 can look like this:

This product’s profit margin is %31.9 (15.91 ÷ 49.90). Since the money tied up in the product is $13.20, ROI is roughly %121 (15.91 ÷ 13.20). If the same product sells with a %10 return rate, you also need to set aside roughly a tenth of the net profit for returns — and the margin suddenly drops toward %28.

To run the same math with your own product’s figures, use the free FBA profit calculator: it shows the net profit, margin, ROI and break-even price in your browser.

The two most-skipped items: returns and currency

Sellers’ hand-built spreadsheets usually include commission and shipping; they rarely include the return rate or currency differences. Yet a %8–10 return rate alone shaves several points off a margin that looks like %30. On the currency side, computing costs at today’s rate but revenue at last month’s rate makes the margin look better or worse than it really is. The correct approach is to convert every transaction into one currency at the rate of its own date, and only then add things up.

How does the math change between FBA and FBM?

The formula is the same; what changes is the logistics item. With FBA it’s Amazon’s fulfillment fee plus storage; with FBM it’s your own shipping plus packaging plus labor. We worked through which model wins for which product in the cost-based FBA/FBM comparison.

5 common mistakes

1. Looking at revenue and saying “I’m making money” — never actually doing the margin math.
2. Treating ad spend as general overhead instead of allocating it to products.
3. Assuming the return rate is zero.
4. Fixing the exchange rate and then hunting for “missing money” at the end of the period.
5. Applying one average margin to every product — the product losing money hides behind the one making it.