Amazon FBA calculator

Most free FBA calculators stop at per-unit profit. This one adds the number that actually decides whether you can afford to advertise the product at all: break-even ACOS, the ad-spend ceiling built directly into your margin, with no separate calculation required.

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Two very different fees sit between the selling price and your profit, and confusing them is the fastest way to misjudge a product before you ever list it.

Amazon updates both fee types roughly once a year, and 2026 added a mid-year complication on top of the usual annual update: fulfillment fees rose an average of $0.08 per unit in the January 2026 update, then a separate 3.5% fuel and logistics surcharge was layered onto every FBA fulfillment fee starting in April 2026. A margin calculated before either change is quietly stale — recalculating after every fee announcement, not just once a year, is what keeps the number real.

Sellers who last checked their margin in 2025 are working from numbers that no longer match what Seller Central actually pays out. The 2026 update wasn't one change but several, landing at different points in the year.

Two practical responses matter more than the individual numbers. First, SIPP (Ships in Product Packaging) certification is becoming more consequential: products not certified to ship in their own retail packaging face additional fees that certified products avoid, making a one-time packaging review worth revisiting for any SKU still shipping in generic Amazon-added packaging. Second, since the fuel and logistics surcharge is a flat 3.5% multiplier on the fulfillment fee rather than a separate line item, it compounds with every other fee change rather than sitting apart from them — a product's total 2026 fulfillment cost isn't last year's number plus $0.08, it's last year's number plus the January increase, multiplied by 1.035 for the April surcharge, plus any seasonal Q4 add-on that applies.

Notice how many categories aren't one flat rate — clothing, jewelry, watches, furniture, and the beauty/baby/grocery group all step down (or up) at a specific price point. That's a real cliff, not a rounding effect: in Clothing & Accessories, an item priced at $19.99 pays 10% ($2.00), while the identical item at $20.01 pays 17% ($3.40) — a $0.02 price change moves the referral fee by $1.40. Jewelry runs the opposite direction: a $249 item pays 20% ($49.80), a $251 item pays 5% ($12.55) on the portion above $250 blended with 20% below it. Pricing a few cents on the wrong side of one of these cliffs changes the fee dramatically, not gradually — worth checking deliberately rather than assuming a smooth percentage curve.

Worked example: a $34.99 item in Home & Kitchen (flat 15%) pays a $5.25 referral fee. The same $34.99 price point in Consumer Electronics (flat 8%) pays $2.80 — a $2.45 swing per unit from category alone, before a single other cost is considered. Confirming the exact category and its fee structure in Seller Central, rather than assuming the commonly cited 15% applies everywhere, is one of the fastest ways to catch a margin estimate that's off before a sourcing decision is made.

Amazon bills FBA storage monthly, based on the average daily cubic feet a product occupies in a fulfillment center — not per unit sold, and not per order. That's what makes it a genuinely different kind of cost from referral and fulfillment fees: it accrues whether or not the product sells that month, and it scales with how long inventory sits, not with sales volume.

The October-to-December jump is the single biggest storage cost lever in the whole FBA fee stack: standard-size storage triples in price for the exact same cubic footage, purely because of the calendar. A seller storing 90 cubic feet of inventory pays $70.20/month from January through September and $216/month during Q4 for identical stock — an extra $145.80 a month for three months, with nothing about the product itself changing.

Two further charges apply on top of the base monthly rate, both worth knowing before they show up as an unexplained line item on a settlement report:

Worked example: a product measuring 0.2 cubic feet, 400 units in stock, stored from July through September (off-peak). Total cubic feet: 0.2 × 400 = 80 cu ft. Monthly storage cost: 80 × $0.78 = $62.40/month, or $0.156 per unit per month. Leave that same inventory sitting through November instead, and the per-unit monthly cost jumps to 80 × $2.40 ÷ 400 = $0.48 — three times higher for the identical stock. Folding a single blended "storage cost per unit" figure into the calculator's other-costs field, without accounting for which months the inventory actually sits in a warehouse, is one of the more common ways a calculated FBA margin quietly overstates the real one heading into Q4.

The practical response most sellers use: clear slow-moving inventory before October 1 rather than let it ride into peak-rate storage, since the same stock sitting through Q4 at $2.40/cu ft can cost more in storage alone than it would to liquidate at a discount in September.

Break-even ACOS is the advertising cost of sale at which ad spend fully consumes what's left of the margin after product and Amazon costs — spend past it and the sale loses money even though it converted. Most PPC guides present this as a separate calculation from product-level profitability; it isn't one.

Same formula, same result, two different questions. Once you've calculated one, you already have the other — which means the moment this calculator returns a margin, it has also just told you the maximum ACOS your PPC campaigns can run before they start burning cash on this product, with no separate spreadsheet required.

In practice, most sellers set a target ACOS meaningfully below the break-even figure — running campaigns right at the ceiling leaves zero room for a bad week, a competitor bid war, or a seasonal CPC spike. A target of roughly 60-75% of break-even ACOS is a common starting discipline: on a 33% break-even ceiling, that's a working target closer to 20-25%, leaving real profit even while running ads, rather than treating break-even itself as the goal.

FBA and FBM aren't a one-time decision made per account — they're a per-product comparison, and the right answer changes with size, weight, and how fast the product turns.

The fastest way to check a specific product: run it through the calculator above with the real FBA fee for its size tier, then run it again with your actual self-fulfillment cost per unit — packaging, postage, and a fair allocation of your own time — in the same field. Whichever run shows the higher net profit per unit is the right call for that product, not a blanket FBA-or-FBM policy applied across the whole catalog.

One point trips up first-time comparisons: the referral fee applies either way — it's Amazon's commission on selling through the marketplace, not a fulfillment charge, so switching from FBA to FBM doesn't remove it. Only the fulfillment line changes. Take a $34.99, 4-pound item with $9 COGS and a 15% referral fee ($5.25): on FBA with a $9.80 fulfillment fee and $1.20 in other costs, total cost is $25.25 and profit is $9.74 — a 27.8% margin. Fulfilling it yourself at $6.50 in real packaging, postage, and labor plus the same $1.20 other costs brings total cost to $21.95 and profit to $13.04 — a 37.3% margin. For this specific weight and price point, FBM wins by almost 10 points of margin; a lighter, faster-turning item at the same price would likely flip the result the other way, which is exactly why this is a per-product check, not a one-time account setting.

Commonly cited FBA benchmarks put a healthy margin at 30% or higher after Amazon fees but before advertising — the 33.0% margin in the worked example above sits right at that line, not comfortably past it.

Margin alone doesn't decide whether a product is worth launching — a low-competition category needing almost no ad spend can work fine at 18-20%, while a crowded category where ranking requires a sustained, aggressive PPC push often needs 35%+ just to leave a workable gap between margin and break-even ACOS. Checking margin against the competitive reality of the category, not a single universal benchmark, is what turns this number into an actual go/no-go decision.

Percentage margin also hides the absolute dollars at stake, which matters more once two products are being compared side by side. A $12.99 item at 35% margin earns about $4.55 per unit; a $49.99 item at 25% margin earns about $12.50 — nearly triple the cash profit despite the lower percentage. Sourcing and advertising decisions built purely around margin percentage can end up favoring the smaller absolute payoff; checking both the percentage and the per-unit dollar figure together is what avoids that trap.

Amazon's fees are all per-unit, but running an FBA business rarely is — software subscriptions, a virtual assistant, an agency retainer, and product photography don't scale down just because a product sells fewer units this month.

The break-even units figure answers a different question than per-unit margin does: not "is this unit profitable," which margin already answers, but "how many units does the whole operation need to move this month before fixed running costs are covered and profit starts becoming real." In the worked example, that's 183 units — a number worth checking against actual sales velocity before assuming the monthly numbers will work out, the same way a seat-capacity or team-capacity check matters for other business types once fixed costs enter the picture.

This figure is single-SKU by design — most FBA sellers run several products whose combined contribution margin covers one shared set of fixed costs, not one product carrying the whole load alone. A seller running three SKUs at $8.24, $5.10, and $3.90 profit per unit, selling roughly 90, 60, and 40 units a month respectively, generates 90 × $8.24 + 60 × $5.10 + 40 × $3.90 = $741.60 + $306.00 + $156.00 = $1,203.60 in combined monthly contribution — against $1,500 in shared fixed costs, that catalog is $296.40 short of break-even even though every individual SKU shows a healthy per-unit margin on its own calculator run. Running each SKU through the calculator and summing contribution dollars, not each product's standalone break-even units, is the more accurate way to check a whole catalog against total monthly overhead.

Run your own FBA numbers above, free, or check the full PPC funnel once you know your break-even ACOS.