Every Amazon seller faces the choice: let Amazon store and ship the product (FBA) or ship it yourself (FBM — fulfilled by merchant). The fee tables make it look like a simple comparison of the FBA fulfillment fee against a postage label. It is not, because each side carries costs the other does not. This guide puts the 2026 numbers side by side for three typical products, then lists the costs that decide the close cases. Rates are from Amazon’s public fee pages, verified 2026-09-20 (data sources).
What each option costs per unit
FBA: referral fee (same either way) + fulfillment fee by size tier and weight (+3.5% surcharge) + monthly storage + inbound freight to Amazon’s warehouse + occasional fees (placement, low-inventory, removals, returns processing).
FBM: referral fee + your postage + packaging materials + labour to pack + storage space you already pay for + your customer-service time. If the buyer pays a shipping charge, the referral fee applies to it as well.
Three products, $10–50 price band
Postage figures are typical 2026 US commercial rates for ground or first-class-equivalent services; yours will differ by carrier contract and zone.
| Small & light — phone case, 4 oz | Medium — kitchen gadget, 1.2 lb | Heavy — 12 lb dumbbell set | |
|---|---|---|---|
| FBA fulfillment fee (2026, + 3.5%) | $3.42 → $3.54 | $5.04 → $5.22 | Large standard 12 lb: $6.97 + 36 × $0.08 = $9.85 → $10.19 |
| FBA storage, 1 month, Jan–Sep | $0.02 | $0.06 | $0.55 (0.7 cu ft) |
| FBA inbound freight (typical) | $0.30 | $0.80 | $3.00 |
| FBA total | $3.86 | $6.08 | $13.74 |
| FBM postage (typical commercial rate) | $4.20 | $7.50 | $14.00 |
| FBM packaging | $0.35 | $0.70 | $1.50 |
| FBM labour (3 min at $20/h) | $1.00 | $1.00 | $1.50 |
| FBM total | $5.55 | $9.20 | $17.00 |
| Difference | FBA cheaper by $1.69 | FBA cheaper by $3.12 | FBA cheaper by $3.26 |
At these assumptions FBA is cheaper across the board — and it comes with Prime, which is why most private-label sellers use it. The picture changes with three things:
- Carrier contracts. A seller shipping 500+ parcels a month with negotiated rates can bring the medium item’s postage to $5.50 and the heavy item’s to $9, at which point FBM is level or ahead for heavy goods.
- Slow inventory. FBA storage is per month. A unit that sits 6 months adds $0.36 (small) to $3.30 (heavy) in storage, plus aged-inventory surcharges from 181 days — and Q4 rates are three times higher. FBM storage in your own garage or 3PL is usually flat.
- Oversize. For large bulky and extra-large tiers ($9.35 + $0.38/lb and $26.33 + $0.38/lb in the $10–50 band, before surcharge), merchant shipping through LTL or a regional carrier is frequently cheaper, and FBA’s oversize storage adds up quickly.
The costs the table hides
On the FBA side
- Inbound placement fees when you send to a single warehouse; low-inventory-level fees when days of supply fall under 28; returns processing fees in high-return categories.
- Returns: FBA refunds the customer first and grades the unit afterwards; unsellable returns are disposed of or shipped back to you for a fee.
- Cash: inbound freight and the fulfillment fee are paid before the sale pays out, and Amazon’s payout lag is about three weeks (see the cash-flow guide).
- Loss of control: co-mingled inventory, warehouse damage claims, and capacity limits in Q4.
On the FBM side
- Time: packing, printing labels, carrier pick-ups, and answering “where is my order” messages. Labour is the item most sellers leave out of the comparison.
- Performance metrics: late shipment rate under 4%, valid tracking rate over 95%, cancellation rate under 2.5% — miss them and the account is at risk.
- Conversion: non-Prime offers convert lower, and the Buy Box favours fast delivery. Seller Fulfilled Prime restores the badge but requires 1–2 day delivery nationwide, which usually costs more than FBA.
- Returns: you pay return postage under Amazon’s prepaid return label policy for most categories.
A rule that holds up
- Standard-size, under 3 lb, selling several units a day, price $15–60 → FBA. The fee is competitive and Prime sells more units; the FBA calculator’s break-even price tells you whether the margin survives.
- Over 5 lb, oversize, or fragile and high-value → cost out FBM with your real carrier rates; FBA’s per-pound charges and oversize storage add up.
- Slow sellers, seasonal stock, large SKU counts with low velocity → FBM or a 3PL; FBA storage and aged-inventory fees punish stock that sits.
- Launching a new product → FBA for the Prime badge and conversion, with an FBM backup offer to keep the listing live.
The Amazon FBA calculator switches between FBA and FBM with your own postage cost, and the marketplace fee comparison shows both alongside Etsy, eBay and Shopify.