| Reason | Fix | Model it |
|---|---|---|
| Freight skipped | Add freight total ÷ units to every estimate | Advanced costs → freight |
| Band jumps | Right-size packaging; test every SKU against 15×12×0.75 in | Enter real dimensions — the tool computes dimensional weight |
| Tier mistakes | Use category-aware tiered rates, not a flat 15% | Pick the category — tiers apply automatically |
| Returns ignored | Amortize category return rate into per-unit cost | Auto-filled from the category return table |
| Storage underestimated | Model inventory days × ft³ × seasonal rate | Advanced costs → storage |
| Ads too high | Set a target ACoS and price against it | Advertising field + margin readout |
| Fuel omitted | Toggle the 3.5% surcharge on (default) | Fuel & logistics toggle |
A $30 home product, 6×4×2 in, 10 oz, $8 landed cost, 10% ads, 60 days storage, minimal placement: ⚡ Try this case live
| Line item | Simple model | Full model |
|---|---|---|
| Referral fee (15%) | $4.50 | $4.50 |
| Fulfillment (0.75 lb) | $4.20 | $4.20 |
| Fuel surcharge | — | $0.15 |
| Advertising (10%) | — | $3.00 |
| Inbound freight | — | $1.50 |
| Returns (8%) | — | $1.35 |
| Storage (60 days) | — | $0.04 |
| Placement | — | $0.30 |
| Total fees + cost | $16.70 | $23.04 |
| Net profit | $13.30 (44.3%) | $6.96 (23.2%) |
The "simple" model shows 44.3% margin — the full model shows 23.2%. The missing $6.34 per unit was never profit; it was cost you weren't counting.
| Category | Referral | Typical net margin |
|---|---|---|
| Consumer electronics | 8% | 25–40% (low referral, but price competition) |
| Home & garden | 15% | 20–30% |
| Beauty (above $10) | 15% | 15–30% (high returns and advertising) |
| Clothing & apparel | 17% | 10–20% (steepest rate + 20–30% returns) |
| Toys | 15% | 20–30% (seasonality risk) |
Enter price, cost, category, dimensions and ad spend — the calculator applies all seven cost buckets and solves your true break-even price. Everything runs in your browser; zero data stored.
Open the calculator with the $30 example →
Related reading: How to Calculate FBA Profit Margin 2026, Six FBA profit calculation mistakes, How to reduce FBA fulfillment fees, Dimensional Weight: Formula & Rules and Amazon FBA Fees 2026: Complete Guide. If a product already turns a loss, see why is my FBA profit negative and how to fix an unprofitable FBA product.
The seven most common causes in 2026: unmodeled inbound freight, dimensional-weight band jumps, referral tier mistakes, ignored return costs, underestimated storage, high ad spend, and the omitted 3.5% fuel surcharge. Together they can silently eat 10–20 points of margin on a typical $30 product.
Divide total shipment cost by units: $300 of freight over 200 units is $1.50 per unit. On a $30 product that is 5% of revenue — the single most commonly skipped cost in free FBA calculators.
Yes. A 10 oz product in a 12×8×4-inch box bills at 384 ÷ 139 = 2.76 lb dimensional weight, landing in the 3 lb large-standard band ($6.67 at the $10–50 price tier) instead of the 0.75 lb band ($4.20) — a $2.47 per-unit difference.
Each return refunds the referral fee, the fulfillment fee and a processing fee — on a $30 home product at an 8% return rate that amortizes to about $1.35 per unit. Apparel's 20–30% rate multiplies the same math by three or four.
PPC spend typically runs 10–30% of revenue depending on category and stage. At 15% ACoS on a $30 product that is $4.50 per unit — nearly as much as the fulfillment fee — so the ACoS you assume in pricing matters more than most sellers think.
Use a calculator that models all seven costs and solves break-even by binary search: the minimum price where net profit reaches zero. The free FBA Calcs calculator does this automatically — price below it and every sale loses money.