"Should we be on FBA or FBM?" is usually asked about the whole business. It's the wrong unit. A small, fast-selling product and a bulky, slow one can sit in the same catalog with completely different economics. Treat the decision as a column in your SKU spreadsheet rather than a company policy, and you'll almost always end up with some of each.
FBA tends to win for small, light, fast-selling products where the Prime badge lifts conversion. FBM tends to win for slow movers, bulky or heavy items, products with long storage times, and anything you also sell on other channels. Decide per SKU by comparing your all-in FBA cost per unit against your FBM cost (fulfillment plus postage), then weigh how much Prime matters for that product. If you choose FBM, you must keep Amazon's seller-fulfilled metrics healthy.
The Two Models in One Paragraph Each
Fulfillment by Amazon (FBA): you send inventory to Amazon's fulfillment centers. Amazon stores it, ships each order, handles customer service and returns for those orders, and your listing gets the Prime badge. You pay fulfillment fees per unit, storage fees, and a growing list of inbound and inventory-related fees. Since January 2026, Amazon no longer preps or labels inventory for US sellers, so units must arrive ready.
Fulfilled by Merchant (FBM): you keep the inventory, in your own space or at a 3PL, and ship Amazon orders yourself. You pay your own fulfillment and postage costs, control packaging, and can serve other channels from the same stock. Standard FBM listings don't carry the Prime badge, and Amazon measures your shipping performance closely.
The Four Factors That Decide It
FBA fees climb steeply with size tier. For small, light items, Amazon's fee is often lower than what you'd pay for postage alone. For bulky items, the gap narrows or flips.
Storage at Amazon is priced to keep inventory moving, with higher Q4 rates and surcharges on aged stock. Products that sit for months pay heavily for it.
In some categories, shoppers barely click on non-Prime offers. In others, especially branded or specialist products, they'll wait an extra day or two.
If a product also sells on your own site or other marketplaces, holding it in one place outside Amazon avoids splitting stock and running out on one channel while it sits in another.
Two Worked Examples
The numbers below are illustrative, chosen to show how the comparison works. Pull your own FBA fees from Seller Central and your own FBM costs from your 3PL quote.
Product A: a small, fast seller
A 7 oz accessory that sells through its inventory in about five weeks.
- FBA: fulfillment fee $3.90, storage $0.10, inbound placement $0.25, prep and labeling $0.20. Total $4.45 per unit.
- FBM via a 3PL: pick and pack $3.10, mailer $0.25, storage $0.05, postage $5.60. Total $9.00 per unit.
FBA wins by more than half, before counting any conversion lift from Prime. This product belongs in FBA.
Product B: a bulky, slow seller
A 6 lb item in a large box that typically sits for eight to ten months before selling.
- FBA: fulfillment fee $9.40, storage across its long stay (including Q4 rates) $6.80, aged inventory surcharge $1.50, inbound placement $0.90, prep $0.40. Total $19.00 per unit.
- FBM via a 3PL: pick and pack $3.60, packaging $1.10, pallet storage $1.20, postage $10.90. Total $16.80 per unit.
FBM saves $2.20 a unit, and frees up FBA capacity for faster products. The open question is whether losing the Prime badge costs more than $2.20 a unit in lost sales. For a specialist product people search for by name, it often doesn't.
Notice that postage is the biggest FBM cost in both examples. Amazon's shipping rates are hard to beat on small parcels. The FBM advantage comes from storage and fee structure, not from cheaper shipping.
A Quick Sorting Guide
If You Choose FBM, Protect These Metrics
With FBM, Amazon is watching how well you ship. Falling below these targets can put your selling privileges at risk, so any 3PL handling your FBM orders needs to treat them as hard requirements.
A few practical habits keep these healthy. Set your handling time to match what your warehouse can do every day, not on a good day. Make sure tracking numbers upload to Amazon automatically, from a carrier Amazon recognizes. And sync inventory often enough that you never sell a unit the warehouse doesn't have, since those cancellations count against you. Our FBM fulfillment service is built around exactly these numbers.
Running Both on the Same Product
You don't have to choose once and forever. You can list the same product under two SKUs, one fulfilled by Amazon and one by you, so an FBM offer is ready to take over when FBA runs out. This is a useful safety net during Q4, when inbound limits and slow check-in can leave you out of stock at Amazon while you have plenty sitting at your 3PL.
Seller Fulfilled Prime is the other middle path: FBM with the Prime badge. It's worth looking at if you have a reliable 3PL and a product where Prime clearly matters, but read Amazon's current requirements carefully before you plan around it.
Frequently Asked Questions
With FBA, Amazon stores your inventory and ships your Amazon orders, and your listing gets the Prime badge. With FBM, you or your 3PL store the inventory and ship Amazon orders yourself, keeping control of packaging and stock, but standard FBM listings don't show the Prime badge.
It depends on the product. FBA is often cheaper for small, light, fast-selling items because Amazon's fulfillment fee can be lower than postage. FBM is often cheaper for bulky, heavy or slow-selling items where storage fees and surcharges add up.
Yes. You can create separate FBA and FBM offers on the same listing under different SKUs. Many sellers keep an FBM offer as a backup so they don't lose sales when FBA inventory runs out.
The key ones are Late Shipment Rate (target under 4%), Pre-fulfillment Cancel Rate (under 2.5%), Valid Tracking Rate (above 95%) and Order Defect Rate (under 1%). Amazon also tracks on-time delivery.
Standard FBM offers lose the Prime advantage and compete on price, delivery promise and seller performance. The effect varies by category. Branded or specialist products are usually less sensitive than generic ones.
Yes. A 3PL can receive your Amazon orders automatically, ship them within your handling time, and upload tracking to Amazon. Confirm its daily cutoff time and on-time shipping record before you hand over FBM volume.
Want FBM without the account-health risk?
We ship FBM orders the same day they come in when they arrive before our cutoff, with valid tracking uploaded on every order. Tell us your volume and handling time and we'll tell you if we can hold it through peak.