FBA Contribution Margin: Formula, Example, Decisions | Inventory Hero
·6 min readProfitability
FBA Contribution Margin: Formula, Example, Decisions
Contribution margin is what each unit contributes after all variable costs. The formula, a worked FBA example, and why it drives which SKUs to fund or cut.
It is the amount each unit contributes after subtracting every variable cost from the selling price: landed cost of goods, Amazon referral and FBA fees, and any per-unit costs like variable shipping. What is left contributes to covering your fixed overhead and then to profit. It is the cleanest measure of what a single sale actually adds to the business.
How do you calculate contribution margin?
Subtract all variable costs per unit from the selling price. For an FBA product selling at 30 dollars with an 8 dollar landed cost, a 4.50 referral fee, and a 5.50 FBA fulfillment fee, variable costs are 18 dollars and the contribution margin is 12 dollars, or 40 percent. Track it in both dollars and percent per SKU.
Andrew Erickson is the founder of Inventory Hero. He has spent years working with Amazon FBA sellers on demand forecasting, restock planning, and the cash flow side of running a private-label brand. Inventory Hero exists because every spreadsheet-based inventory system he tried eventually broke — usually right before Q4.
What is the difference between contribution margin and gross margin?
Contribution margin subtracts all variable costs, including Amazon fees and per-unit shipping, so it reflects what a sale truly contributes on FBA. Gross margin traditionally subtracts only cost of goods sold and can overstate profitability if it ignores fees. Net margin goes further and subtracts fixed costs too. Contribution margin is the most useful for per-SKU funding decisions.
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Contribution margin is the money each unit contributes after you subtract every variable cost from its selling price. On FBA that means price minus landed cost, minus Amazon's referral and fulfillment fees, minus any per-unit variable cost. What is left is what the sale actually adds to covering your overhead and then to profit. The short version: it is the number that should drive which SKUs you fund, keep, or cut, because it tells you what each sale truly contributes rather than what a rosier margin figure implies. Below is the formula, a worked FBA example, and how it differs from the other margins.
Landed cost of the unit. This is usually the hardest number to get right: it is the FOB factory price plus ocean freight, duties, and inbound FBA shipping, divided by the units in the shipment, not the factory invoice alone.
Per-unit advertising cost. Include it: divide your total ad spend on the SKU by the units it sold in the period. PPC is a real variable cost, and leaving it out is the single most common way a SKU looks like a 40 percent winner while actually running at 20 percent once ads are counted.
Other per-unit variable costs: prep and any variable shipping.
Fixed costs (software, salaries, your own overhead) are deliberately left out, because contribution margin measures what one more sale adds, and one more sale does not change your fixed costs.
This SKU contributes 12 dollars, or 40 percent, before advertising. Now add PPC, because it is the line that most often flips the verdict: if this SKU carries 3 dollars of ad spend per unit sold, its real contribution margin is 9 dollars, or 30 percent, not 40. That is the difference between a strong SKU and a merely acceptable one, and it is invisible until you include ads. Cite the referral and FBA fees from your own Amazon fee preview for the specific SKU rather than a flat estimate, because both vary by category and size.1
These three margins answer different questions, and mixing them up leads to bad decisions:
Contribution margin subtracts all variable costs, including fees. It answers "what does one more sale of this SKU add?" Best for per-SKU funding and pricing calls.
Gross margin traditionally subtracts only cost of goods. It can overstate FBA profitability if it ignores fees, so treat it carefully.
Net profit margin subtracts fixed costs too. It answers "is the whole business profitable?" Best read at the account level.
For day-to-day SKU decisions, contribution margin is the one that keeps you honest, because it captures the fees that quietly eat FBA profit. The gap is not small. Run the same 30 dollar SKU both ways:
Measure
Calculation
Result
Gross margin (COGS only)
30 - 8
$22 (73%)
Contribution margin (all variable costs)
30 - 8 - 4.50 - 5.50 - 3
$9 (30%)
A SKU that looks like a 73 percent gross-margin star is a 30 percent contributor once fees and ads are in. That 43-point gap is exactly the illusion contribution margin exists to kill.
Track contribution margin both ways, because each answers a different question:
Contribution margin in dollars is cash contribution. A 12 dollar CM on a high-volume SKU can fund the business even at a modest percentage.
Contribution margin in percent is efficiency. A 40 percent CM tells you how much of each sales dollar survives variable costs, which matters most when cash or ad budget is tight.
A common trap is chasing high-percentage SKUs that sell in tiny volumes; the dollars are what pay the bills. Read both, per SKU.
As a rough anchor, private-label FBA contribution margins after fees and ads commonly land in the 20 to 40 percent range; below about 15 percent leaves too little cushion for storage, returns, and the odd fee increase to absorb.2 There is no universal target, so track your own trend quarter over quarter rather than comparing across categories.
Contribution margin is also what tells you how much you have to sell to cover your fixed costs. Because each unit contributes its margin toward overhead, your break-even volume is:
Break-even units = fixed costs / contribution margin per unit
If your monthly fixed costs (software, VA, your own draw, storage overhead) come to 6,000 dollars and the SKU above contributes 12 dollars a unit, you need to sell 6,000 / 12 = 500 units a month on that product to break even on fixed costs. Sell more and the contribution above break-even is profit; sell fewer and you are covering variable costs but not the overhead.
This is why contribution margin in dollars matters as much as percent: a high-percentage SKU that only moves a handful of units contributes little toward the fixed nut, while a moderate-percentage SKU at volume can carry the business. Run the break-even on your top SKUs and you will see quickly which products are actually keeping the lights on.
Contribution margin turns into decisions directly:
Fund the SKUs with the strongest contribution in dollars first when reorder cash is limited; pair it with GMROI to weigh the cash they tie up and the cash conversion cycle to see how long that cash stays locked per turn.
Fix low-CM SKUs by repricing, renegotiating landed cost, or reducing fees through better sizing.
Cut SKUs whose contribution margin no longer covers the attention and cash they consume.
Contribution margin is price minus every variable cost, the true measure of what each FBA sale adds to overhead and profit. Track it per SKU in both dollars and percent, keep it distinct from gross and net margin, and let it drive which products you fund and which you cut. It is a core input to your wider FBA cash flow and the inventory KPIs that sit alongside it.
Referral fees are set by Amazon's fee schedule; 15 percent is the standard rate for many categories (effective 2024-01-15) but ranges roughly 8 to 45 percent by category. The FBA fulfillment fee in the example is illustrative and varies by size and weight tier. Pull both from your own FBA fee preview per SKU. Source: Amazon Seller Central fee schedules. ↩
The 20 to 40 percent contribution-margin range is a private-label operator rule of thumb, not a measured or Amazon-published figure. It varies widely by category and ad reliance; use it as orientation and track your own trend. ↩