Is Amazon FBA Worth It? Calculate Your Real Profit Margin.

Amazon FBA charges: (1) Referral fee: 6–20% of selling price depending on category (most categories 15%); (2) FBA fulfillment fee: $3.06–$150+ per unit based on weight and size tier; (3) Monthly inventory storage fees: $0.83/cubic ft (standard season) or $2.40/cubic ft (Q4); (4) Long-term storage fees: additional charges for units stored 365+ days; (5) Inbound placement fees for shipping inventory to multiple fulfillment centers; (6) Returns processing fees for returned items. The fulfillment fee is the one sellers most commonly underestimate — use Amazon's FBA Revenue Calculator for the exact amount for your ASIN.

A healthy FBA margin is generally 25–40%+ after all fees. Below 20%, small cost increases (shipping rate, COGS, storage) quickly turn profitable products negative. More important than margin alone is ROI (return on investment): how much profit you earn per dollar of inventory invested. A 30% margin on a product you turn monthly generates 12× as much annual ROI as the same margin on a product that takes 4 months to turn. The sweet spot most experienced FBA sellers target: 30%+ margin AND 100%+ annual ROI.

ACoS (Advertising Cost of Sale) is the percentage of revenue spent on Amazon PPC advertising. If you spend $1 on ads that generates $5 in sales, your ACoS is 20%. Your break-even ACoS is your profit margin — if you're making 35% margin, any ACoS below 35% adds to profit; above 35%, you're losing money on advertised sales. The calculator lets you enter a per-unit PPC cost (your total monthly ad spend ÷ monthly units sold) to see the full impact on profit per unit.

FBA (Fulfilled by Amazon): Amazon warehouses your inventory and handles shipping, customer service, and returns. You pay fulfillment fees (~$3–$8+ per unit) but get Prime eligibility and Amazon handles logistics. FBM (Fulfilled by Merchant): You store and ship inventory yourself. No FBA fulfillment fees, but you handle shipping costs, customer service, and returns, and typically lose Prime badge visibility. FBM works well for large/heavy items where FBA fees are proportionally large, or for products with slow velocity where storage fees accumulate. The profit calculation differs significantly between the two models.

The most accurate method: use Amazon's FBA Revenue Calculator (available in Seller Central) and enter your specific ASIN or product details. The fee depends on whether your product is a standard-size or oversize item, and within that, on the dimensional weight (calculated as length × width × height ÷ 139). Standard-size items under 1 lb pay around $3.06; items 1–2 lbs pay around $4.99; oversize items start at $9.73 and increase rapidly with weight. Underestimating this number is one of the most common causes of FBA products performing worse than projected.