Amazon FBA US is the highest-stake, most-complex marketplace for US sellers. Three layered fees (referral + fulfillment + storage) plus optional plan costs plus sales tax plus PPC ad spend create a margin maze where successful sellers operate on tight calculation. The calculator above unwinds the layers.
The three core fees
Referral fee (% of sale, by category): - Most categories: 15% - Electronics, Computers: 7% - Health & Household, Grocery: 8% - Jewelry: 20% (under $250) / 5% (above) - Watches: 15% (under $1,000) / 5% (above) - Beauty: 8% (under $10) / 15% (above) - Amazon Device Accessories: 45% (highest on platform)
Fulfillment fee (flat $ by size and weight): - Small envelope (≤80g): $1.93 - Standard parcel (≤500g): $2.92 - Heavy parcel (≤9kg): $3.65 - Standard parcel (≤12kg): $5.30 - Oversize - small (≤25kg): $8.95
Storage fee ($ per cubic foot per month): - Standard, Jan-Sep: $0.55 - Standard, Oct-Dec: $0.79 (45% premium for Q4 peak) - Oversize, Jan-Sep: $0.45 - Oversize, Oct-Dec: $0.65
Plus Selling Plan: Individual $0.75/unit (no monthly fee) OR Professional $25/month (no per-unit fee). Breakeven ~33 units/month.
Plus state sales tax (where applicable) on all fees in states with sales tax on services.
Margin maths reality check
For a $20 product: - Referral 15%: $3.00 - Fulfillment small parcel: $2.92 - Storage (0.05 ft³, standard): $0.03 - Pro plan (100/month): $0.25 - Subtotal: $6.20 - state sales tax on fees (where applicable): $1.24 - Total Amazon fees: $7.44 - Pre-COGS take: $12.56 (62.8% retention)
For COGS of $6, profit is $6.56 — 32.8% margin. That’s the FBA reality at this price point: ~30-35% margin is the achievable healthy range for sub-$25 items.
When FBA stops making sense
Below $8-10 retail, FBA fees consume too much margin to compete. Books, low-priced media, sub-$10 accessories: consider Amazon MFN (Merchant Fulfilled — you pack and ship). MFN saves the $2-$3 fulfillment fee per unit, allowing competitive pricing on slim-margin items. The trade-off: no Prime badge, slower delivery, and you handle returns directly.
Above $100 retail with low referral rate (Electronics, Computers): FBA economics are excellent. $100 × 7% = $7 referral; even with fulfillment + storage the Amazon take is ~10-12% of sale price. These are FBA’s sweet spots.
Sales tax on platform fees (varies by state)
Sellers in states with sales tax pay state sales tax on platform fees can apply in some states. For a seller doing $8/unit in fees, that’s $1.60 of unrecoverable sales tax per unit. Stack across 100 units/month and $160/month leaks straight to IRS.
Most US states require Amazon to collect and remit sales tax on your behalf via marketplace facilitator laws. Direct registration is usually only positive — even before the $90k threshold. Consider TaxJar or Avalara for state-specific calculations.
What the calculator excludes
- Returns (5-15% typical, eat 1-3pp of margin)
- PPC ad spend ($100-$500/month minimum to stay competitive)
- Long-Term Storage Fees (items > 365 days)
- Inbound Placement Service (~$0.30/unit for distributed inbound)
- FBA Small & Light (slightly different fee schedule for sub-$11 items)
- Sale-side sales tax on the customer transaction (handled separately)
For combined PPC + FBA profitability, run ROAS calculator on your ad spend, then subtract from this calculator’s profit per unit. For tax treatment, FBA fees are fully deductible — see the side hustle tax calculator.
From FBA fees to a real ad-spend ceiling
Knowing your profit per unit after FBA fees is only half the picture for most active sellers, since PPC is usually running alongside organic sales. The number that connects the two is break-even ACOS — the percentage of a sale's revenue you can spend on Amazon Ads before that unit stops being profitable. It's calculated directly from the fee output above: take sale price, subtract COGS, subtract referral fee, subtract fulfilment fee, and what's left as a percentage of sale price is your ad-spend ceiling. The PPC break-even ACOS calculator takes this calculator's fee output and turns it into that ceiling plus a max CPC bid, so you're not guessing at what to type into the bid box.
FBA vs FBM — the fee trade-off in practice
The three core FBA fees this calculator computes (referral, fulfilment, storage) don't exist under FBM (Fulfilled by Merchant) — but FBM isn't free either, it just shifts the cost from Amazon's fee schedule to your own shipping and labor costs. A rough way to compare: total FBA cost per unit (referral + fulfilment + storage share) against your actual cost to pack and ship that same unit yourself, including your own packaging materials, your time valued at a real hourly rate, and whatever carrier rate you can negotiate. For low-cost, lightweight items with strong FBA size-tier pricing, FBA usually wins on pure economics once Prime eligibility and Buy Box weighting are factored in. For bulky, heavy, or slow-moving items, the FBA storage and fulfilment fees can exceed what efficient in-house fulfilment would cost — this is exactly the calculation worth running before committing inventory to either model, not after.
The 2026 Small Bulky tier — who it actually helps
Amazon's 2026 fee update introduced a new "Small Bulky" size tier specifically for items in the 3-50 lb range with a longest side of 18-37 inches — a category that previously fell into the more expensive Large Bulky fulfilment fee bracket. The new tier represents roughly a 22% fee reduction for items that qualify versus the old Large Bulky rate. This matters most for sellers of moderately bulky home goods, sporting equipment, and larger toys — items that were previously penalized by a fee bracket built around genuinely oversized furniture and appliances rather than their actual size. If your product sits anywhere near that 3-50 lb, 18-37 inch boundary, it's worth re-checking which size tier it now falls into, since a product that was Large Bulky under the old schedule may now qualify for the cheaper Small Bulky rate.