FBA vs FBM: How Fees and Your Margin Change per Product

The difference between FBA and FBM comes down to who stores, packs, and ships your product: with FBA (Fulfillment by Amazon), Amazon does it from its fulfillment centers, which is why you pay fba fees for storage and per-unit fulfillment; with FBM (Fulfillment by Merchant), you or your 3PL handle it, so those Amazon fees disappear but you absorb the real cost of warehousing, packing, and carrier shipping. The referral fee is paid identically in both models; what changes — and sometimes flips your margin — is everything else.

That’s why “FBA or FBM?” has no single answer for your account: it has one product by product. A light, small, fast-moving item usually wins with FBA because the fba fees stay low and you buy yourself the Buy Box, Prime, and fast shipping. A bulky, heavy, or slow-moving product can bleed under FBA on storage and oversize surcharges, and leave more margin if you ship it yourself. The right model is the one that leaves more net dollars in your pocket for that SKU — not the one that feels more convenient.

The hard part is seeing that number clearly. Fba fees change by weight, dimensions, and season; the FBM cost depends on the rate you negotiated with your carrier and on what it costs you to store the box. Pulling all of that together by hand, in a spreadsheet that’s already out of date, to decide channel by channel — that’s exactly where the multichannel seller gets lost.

what fees each model pays

Let’s separate what’s the same from what changes. In both models you pay the referral fee: a percentage of the sale price that varies by category (typically between 8% and 20%). You don’t get to set it, and you don’t dodge it by switching logistics.

What you pay only in FBA:

• Fulfillment fee: a per-unit charge for picking, packing, and shipping each order, calculated by weight and dimensions. This is the heart of the fba fees.
• Monthly storage: rent for the space your inventory takes up in Amazon’s center, more expensive in peak season (the last months of the year).
• Long-term storage: a surcharge if your product sits for months without selling. It punishes slow rotation.
• Inbound (shipping to the center): what it costs you to send inventory to Amazon before it starts selling.

What you pay only in FBM:

• Your warehouse: rent, utilities, staff — or your 3PL rate if you outsource.
• Packing and prep: boxes, materials, the labor to assemble each order.
• Carrier shipping: the shipping label, which depends on your volume and what you negotiated with the carrier.
• Returns and support: in FBM you handle them, with the operational cost that implies.

The trap is believing “FBM has no fees.” It does; they just don’t show up on an Amazon statement — they’re scattered across your own books. Comparing well means putting both cost columns side by side, for the same product.

why weight and volume decide almost everything

The fba fees for fulfillment and storage scale with size and weight. That creates a practical rule: the smaller and lighter your product, the cheaper FBA gets; the bigger and heavier it is, the faster FBA stops making sense.

An 80-gram phone charger pays a minimum fulfillment fee and takes up a laughably small amount of warehouse space. There FBA almost always wins: the fba fees are low against the price, and in exchange you get Prime, fast shipping, and a strong edge for the Buy Box. Shipping it yourself would cost you more in carrier fees than Amazon charges per unit.

A 6-kilo monitor stand is the opposite story. The fulfillment fee climbs, monthly storage bites hard because it eats volume, and if it rotates slowly the long-term surcharge kicks in. That same product, shipped by you with a negotiated carrier rate, can leave considerably more margin — as long as your operation handles the volume without errors.

Glossary: real net margin, everything deducted →

rotation: FBA’s silent cost

There’s one fee that bites without warning: long-term storage. A product that sits for months in Amazon’s center racks up monthly rent and, past a certain point, a surcharge that can turn a winner into a loser. In FBA, inventory that doesn’t move costs you — even if you don’t sell a single unit.

In FBM that cost exists too — your warehouse isn’t free — but it’s usually flatter and cheaper per unit for slow-moving product. So a useful rule: high-rotation products tend to favor FBA (you move fast, you never hit long-term storage, you win Prime); low-rotation or seasonal ones often call for FBM, so you don’t rent Amazon space for a product that just sits there.

This is where the model connects to your real-time inventory: without knowing how fast each SKU rotates and how many days of stock you have left, you pick the channel blind. Sell-through isn’t an “ops” detail; it’s the variable that decides whether the fba fees for storage help you or sink you.

the same product, two margins

Let’s put it in numbers for a product selling at $499:

Item	FBA	FBM
Sale price	$499	$499
Product cost	−$180	−$180
Referral fee (~15%)	−$75	−$75
Fulfillment / carrier	−$70	−$95
Storage / warehouse	−$25	−$12
Returns (provision)	−$20	−$25
Net margin	$129 (26%)	$112 (22%)

In this example (small, medium rotation) FBA wins narrowly: the fba fees for fulfillment are pricier than your warehouse, but your carrier costs more than Amazon’s per-unit rate, and FBA ends up on top. Change the weight to 6 kilos and it all flips: FBA’s fulfillment spikes, storage too, and FBM starts leaving more margin. Same table format, opposite results depending on the product. That’s why the decision is per SKU, not per account.

the model isn’t fixed: it shifts with season and price

A common mistake is treating FBA vs FBM as a one-time decision. It isn’t. The fba fees for storage rise in peak season, so a product that made sense in FBA in March might make sense in FBM in November. A price change also moves the break-even point: raise the price and you absorb the FBA fee better; drop it for a promo and the fba fees weigh more, so FBM may hold the offer better.

This ties into how you run pricing. If you build an aggressive offer with a price calendar, you have to check whether the margin still stands with the fba fees of the channel you chose — a promo that looks healthy in FBM can end up at a loss in FBA because of the fixed per-unit fee.

Glossary: what a price calendar is and why to automate it →

don’t forget VAT and returns

Two line items that get left out of almost every comparison and change the outcome. VAT (16%) must be handled correctly in both models; it isn’t a logistics fee, but if you don’t prorate it right you’ll compare two margins where neither is real. And returns: in FBA, Amazon processes them (with its associated cost and the risk that the unit comes back unsellable); in FBM you handle them, with your own operation and your own cost. On products with a high return rate, that column can tip the scale as much as the fba fees.

Comparing FBA vs FBM well, then, means comparing complete net margins, not loose fees. Referral fee + fulfillment (or carrier) + storage (or warehouse) + inbound + returns + VAT, for the same product, in each model. Only when you put those two full columns side by side do you see which one actually leaves more money. VAT on marketplaces is a piece that, counted wrong, distorts the whole comparison.

Glossary: laddered offer, step by step →

from gut feel to a per-SKU number

The multichannel seller lives this decision daily and usually settles it by instinct or habit: “everything goes to FBA because it’s easier.” Sometimes that’s the right call; sometimes you’re renting Amazon a warehouse for a product that doesn’t rotate, or paying premium fulfillment for something you’d ship cheaper yourself. The cost of deciding blind doesn’t show up in a single order — it shows up at month’s end, when the margin doesn’t match what you “felt.”

The way out isn’t a bigger spreadsheet. It’s seeing, per product and per channel, the real net margin with the fba fees, carrier, storage, returns, and VAT already deducted — and in real time, because rates and rotation change. That’s when “FBA or FBM?” stops being a bet and becomes a reading: the model that wins is the one the table shows in black, for that SKU, today. That’s what iqseller computes per product and per channel, without you having to gather the information by hand.