How to Calculate Amazon FBA Profit Before You Buy Inventory

The fastest way to lose money selling on Amazon is to buy inventory without knowing your true profit per unit. Between referral fees, fulfilment fees, storage and the cost of goods, a product that looks profitable at first glance can quietly lose money on every sale. This guide walks through exactly how to calculate your real Amazon FBA profit and margin before you commit to stock, so you only buy products that actually make money.

The FBA profit formula

At its simplest, your profit per unit is the price you sell at, minus every cost of selling it:

Profit = Selling price − Referral fee − Fulfilment fee − Cost of goods − Other costs.

Your margin is that profit expressed as a percentage of the selling price. A healthy FBA product typically aims for a margin that leaves real room after advertising and the occasional return — many sellers target a net margin comfortably into double digits. The Amazon FBA Calculator works all of this out for you in seconds.

The two big Amazon fees

Referral fee

Amazon takes a referral fee on every sale — a percentage of the selling price that varies by category, commonly around 15%. This is effectively Amazon's commission for the sale and applies whether or not you use FBA.

Fulfilment fee

If you use Fulfilment by Amazon, you also pay a fulfilment fee for picking, packing and shipping each unit. This depends on the item's size and weight, so bulky or heavy products cost much more to fulfil. Getting the dimensions right in your calculation is essential, because underestimating this fee is a classic way to turn a "profitable" product into a loss-maker.

The hidden costs that catch sellers out

The two headline fees are only part of the picture. Before you trust a profit figure, account for:

• Storage fees — charged monthly, and much higher in peak season.
• Advertising (PPC) — most products need ads to get visibility, and this cost per sale can be significant.
• Returns and refunds — some categories see high return rates.
• Inbound shipping — getting your stock to Amazon's warehouses.
• Long-term storage fees if inventory sits unsold.

A product with a slim margin before these costs can easily be unprofitable after them.

A worked approach

Start with your selling price. Subtract the referral fee percentage for your category. Subtract the fulfilment fee for your product's size tier. Subtract your landed cost of goods — the manufacturing price plus inbound shipping and duties. What remains is your gross profit per unit. Now subtract an honest estimate for advertising and returns. If the number is still comfortably positive, you have a viable product. If it is marginal, a single price drop by a competitor could wipe out your profit.

Tips for protecting your margin

• Favour small, light products to keep fulfilment fees low.
• Negotiate your cost of goods — every unit of saving is pure margin.
• Model a worst case with higher ad costs and returns before ordering.
• Recalculate whenever Amazon changes its fees, which happens regularly.

Conclusion

Profitable Amazon selling starts with honest maths done before you buy. Account for the referral fee, the size-based fulfilment fee, and the hidden costs of storage, ads and returns — then only commit to products that still make money with room to spare. Run your numbers now with the free Amazon FBA Calculator and never order inventory on a hunch again.

FBA vs FBM: a cost comparison

Fulfilment by Amazon (FBA) is not the only option — Fulfilment by Merchant (FBM), where you ship orders yourself, can be more profitable for some products. FBA saves you time and gives your listings the Prime badge, but the fulfilment and storage fees are significant, especially for large or slow-selling items. FBM avoids those fees but costs you time, packaging and your own shipping rates, and usually means no Prime badge. As a rough guide, small, fast-selling items often win with FBA, while bulky, heavy or slow movers can be cheaper via FBM. Run both scenarios in the calculator before deciding — the fulfilment method can swing a product from loss to profit.

Frequently asked questions

How do I calculate Amazon FBA profit?

Subtract the referral fee, fulfilment fee, cost of goods and other costs from your selling price. What remains is your profit per unit, and expressing it as a percentage of the price gives your margin.

What are the main Amazon FBA fees?

The two biggest are the referral fee (a category-based percentage of the sale, often around 15%) and the fulfilment fee (based on the item's size and weight). Storage and advertising add further costs.

What margin should I aim for on FBA?

Aim for a net margin that stays healthy after advertising and returns — many sellers target comfortably into double digits. A thin margin leaves no room for a competitor's price cut.

Are these fee calculators exact?

They use Amazon's standard published fee structures, so treat the result as a close estimate. Confirm against your own Seller Central figures for the precise numbers, as fees change over time.