Why the FBA calculator says you'll lose money
Last updated
Almost always one of two input mistakes, not a real loss. Check inbound freight first, then check whether the FBM number you're comparing against includes the shipping you charge customers.
Check these two fields first
- Inbound freight to Amazon. This field wants a per-unit cost, and it is the single most common reason the calculator returns a frightening number. Sellers who don't yet know their per-unit rate often type in the invoice for the whole shipment instead - dropping in $250 for a pallet of 500 units when the real per-unit figure is $0.50. That one field can single-handedly erase your margin on paper.
- FBM revenue basis. If you're comparing against selling the item yourself, make sure the revenue side includes shipping the customer pays you, not just the item price. A $18.50 item with $7.95 charged for postage is a $26.45 sale, not $18.50 - and Amazon's referral fee is calculated on the full amount either way, so understating your own revenue while Amazon's math stays consistent is what tips a real comparison into a false loss.
Both mistakes point the same direction: they make FBA look worse than it is. Fix them before concluding the product doesn't work under FBA.
The whole-shipment mistake, worked
This is the exact error behind a well-known seller thread: a shipment of 20 units cost $8.80 to send to Amazon in total. Entered as-is, that reads as $8.80 of inbound freight on every single unit - a cost nobody would actually accept. Divided correctly:
$8.80 total ÷ 20 units = $0.44 per unit
The seller had priced at $18.50 with $7.95 flat-rate shipping and got a scary result from Amazon's calculator; the shipment-total entry, not the product, was the problem. Once corrected, the real per-unit freight was under fifty cents.
If you don't know your per-unit rate yet, don't guess it - divide your actual invoice. The FBA fee calculator and the FBA vs FBM calculator both take the shipment total and the unit count directly and do this division for you, next to the field it feeds.
The FBM revenue mistake, worked
Using the same numbers: an $18.50 item with $7.95 charged for shipping is a $26.45 sale under FBM, because the customer paid $26.45 to get the product. Compare that against an $18.50-only figure and FBM looks stronger than it is - which makes switching to FBA look like a loss by comparison, even before any fee is counted. The FBA vs FBM calculator flags this directly next to the shared sale-price field, and lets you set a separate price for the FBA offer if it differs.
If both fields are already right
Then the loss may be real, and worth checking for one of three ordinary causes rather than a calculator bug: a size tier or weight above what the product actually needs (get an exact figure from the fee calculator), a price that hasn't been raised to absorb Amazon's fees, or a monthly-volume comparison being made on a single unit's profit. FBM often wins on a per-unit basis while FBA still wins on the monthly total, because the Prime badge tends to sell more units of the same listing - the FBA vs FBM calculator is built to surface exactly that trade-off instead of the per-unit number alone.
Questions
Why does the FBA calculator show a big loss on a product I already sell profitably?
Almost always because of one input, not the product: inbound freight entered as the cost of the whole shipment instead of the cost per unit. A $250 pallet shipment typed straight into a per-unit field reads as $250 of freight on every single item, which will show a loss on nearly anything.
Divide your shipment invoice by the number of units in it before entering it, or use a calculator with a built-in converter, such as the FBA vs FBM calculator, which takes the invoice total and unit count and fills in the per-unit field for you.
What do I put in the inbound shipping field of an FBA calculator?
The cost to ship one unit to Amazon's warehouse, not the cost of the shipment as a whole. If a box of 20 units cost $8.80 to send in total, the field wants $0.44 - the $8.80 divided by the 20 units, not the $8.80 itself.
If you don't know the per-unit figure yet, take your last inbound shipping invoice and divide its total by how many units were in that shipment. That is your rate until your carrier or shipment size changes.
Should FBM revenue include the shipping I charge customers?
Yes. If a customer pays $18.50 for the item plus $7.95 for shipping, your FBM revenue on that sale is $26.45, not $18.50 - that's the total the customer actually paid you. Leaving the shipping charge out understates FBM revenue and makes any comparison against FBA look more favorable to FBA than it really is.
This matters most when comparing routes: if your FBA offer removes a separate shipping charge and folds it into the listed price instead, make sure both sides of the comparison are being priced by what the customer actually pays in total, not by two different bases.
My inbound freight really is expensive - is that number wrong too?
Not necessarily. Bulky, heavy, or long-distance and international shipments can have a genuinely high per-unit freight cost, and the calculator has no way to know your product is an outlier. The question isn't whether the number is high, it's whether it's a per-unit figure at all - a legitimately high per-unit freight cost and an accidental whole-shipment total can look identical to the calculator.
Recheck the arithmetic: total invoice divided by units shipped. If that division genuinely produces a high number, the freight cost is real and belongs in the comparison as-is.
Could the product's size tier or weight be the real reason for the loss?
Yes, and it's worth ruling out once the two input mistakes above are fixed. Amazon bills fulfillment on the greater of actual weight and dimensional weight (length × width × height in inches, divided by 139), so a small but boxy product can be billed heavier than it feels. An oversized tier carries a materially higher fulfillment fee than the tier just below it.
Run the exact dimensions and weight through the FBA fee calculator to see the size tier it lands in and the fulfillment fee that tier carries, rather than assuming the size tier picked on a guess is correct.
FBA loses money per unit but I'd sell more of them - does that change the answer?
Often, yes. Per-unit profit and monthly profit are different questions, and a product can lose on the first while winning on the second. FBM frequently wins per unit, because your own postage and packaging can undercut Amazon's fulfillment fee - but FBA frequently wins per month anyway, because the Prime badge tends to convert more of the same traffic into orders.
The FBA vs FBM calculator models this directly: enter your expected sales lift from the Prime badge and it reports the monthly profit for both routes, plus the exact breakeven lift at which FBA overtakes FBM for your numbers.
Run your own numbers: the free FBA profit calculator models fees, storage, and cost of capital per unit - no signup, nothing leaves your browser.