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.