FBA (Fulfilment by Amazon) and FBM (Fulfilment by Merchant) are the two fulfilment models on Amazon. With FBA, Amazon stores and ships; with FBM, the seller does it themselves. For the profit calculation, these are two different worlds.
What is the difference between the two models?
With FBA, the goods sit in Amazon's warehouse. Amazon takes care of packaging, shipping and a large part of customer service, and charges fulfilment and storage fees for it. The item is Prime-eligible.
With FBM, the goods stay with the seller. Instead of the FBA fees, you have your own shipping and packaging costs, which vary by shipment and carrier. In return, there are no storage fees and no dependence on Amazon's inventory.
Why do FBA and FBM have to be calculated separately?
Because the cost structures are not comparable. With FBA, the costs depend on the item's dimensions and weight and appear as a fee in the settlement; with FBM, they depend on the chosen shipping method and appear only in your own records. An average across both models gives a figure that is wrong for both cases.
Then there is storage: FBA storage fees and the aged inventory surcharge arise even when nothing sells. They therefore belong to the costs an item causes without appearing in any order.
What happens with a return?
This is where the models differ most clearly. If an order is refunded, Amazon credits the referral fee minus a refund administration fee of 20%, capped at €5.00. The FBA fulfilment fee for the original shipment is not credited. So a return costs more than the lost revenue, and differently for FBA than for FBM.
FBA and FBM separated in the contribution margin
profitkonsole for Amazon calculates both models by their own rules and reports them separately: fees per SKU from your settlement data, shipping costs from your own entries.
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Contribution margin, not revenue
Every sales channel in one dashboard: marketplace data and your own costs brought together, per item and per channel.