An FBA vs FBM calculator only has to answer one question: is your all-in cost to ship one unit yourself lower than Amazon’s all-in cost to ship it for you? The break-even point is the FBM postage label at which the two sides tie — break-even postage = FBA fulfillment fee + FBA storage per unit + inbound placement and prep per unit − your own packing, labor, and storage per unit. If your real label costs less than that number, FBM keeps more margin on that SKU; if it costs more, FBA does. Then one second check decides whether the Prime badge on FBA sells enough extra units to overturn a small FBM saving.
Our FBA vs FBM comparison covers which products lean each way, and our free FBA fee calculator roundup covers which tools to trust. This guide is the math behind both: the formula, the current US rate lines (data checked 2026-09-26), and three worked products.
The Break-Even Formula in One Line
Line up only the costs that differ between the two methods. Anything you pay either way drops out.
| Cost line | FBA side | FBM side |
|---|---|---|
| Referral fee | Paid | Paid (same rate, same price) |
| Selling plan | Paid | Paid |
| Cost of goods, freight from supplier | Paid | Paid |
| Last-mile shipping to buyer | Inside the FBA fulfillment fee | Your postage label |
| Pick, pack, box, customer service, returns handling | Inside the FBA fulfillment fee | Your packaging, labor, and returns time |
| Storage | Amazon monthly storage per cubic foot | Your shelf, garage, or 3PL rate |
| Getting stock into the network | Inbound placement, prep, labeling | Usually nothing extra |
The referral fee is the line most sellers wrongly put in the comparison. At the same price in the same category, Amazon’s referral fee is identical whether you or Amazon ship the order, so it cancels. (It stops cancelling in three specific cases, covered further down.)
What remains gives two formulas:
FBA cost per unit = fulfillment fee × 1.035 + storage per unit + inbound placement and prep per unit
FBM cost per unit = postage + packaging and labor + your storage per unit + returns handling per unit
Set them equal and solve for postage, and you have the break-even:
Break-even postage = FBA cost per unit − (packaging and labor + your storage + returns handling)
The × 1.035 is not optional in 2026. Amazon’s fee page states that starting April 17, 2026, “a 3.5% fuel and logistics-related surcharge will be applied to fulfillment fees across Fulfillment by Amazon (FBA) in the US” (Seller Central, data checked 2026-09-26). The published rate card excludes it, so a calculation that reads the rate card at face value understates FBA by 3.5%.
Step 1: Read Your FBA Fulfillment Fee Off Amazon’s Rate Card
The fulfillment fee is set by three things: size tier, shipping weight, and price band. Amazon’s US rate card for January 15 to October 14, 2026 (non-apparel, non-dangerous goods, surcharge not included) reads as follows for the rows most sellers land in:
| Size tier | Shipping weight | Under $10 | $10–$50 | Over $50 |
|---|---|---|---|---|
| Small standard | 10+ to 12 oz | $2.82 | $3.78 | $4.04 |
| Small standard | 14+ to 16 oz | $2.95 | $3.96 | $4.22 |
| Large standard | 1+ to 1.25 lb | $4.22 | $5.04 | $5.30 |
| Large standard | 2+ to 2.25 lb | $5.10 | $5.92 | $6.18 |
| Large standard | 3+ to 20 lb | $6.15 + $0.08 per 4 oz above 3 lb | $6.97 + $0.08 per 4 oz above 3 lb | $7.23 + $0.08 per 4 oz above 3 lb |
| Small Bulky | 0 to 50 lb | $6.78 + $0.38/lb above first lb | $7.55 + $0.38/lb above first lb | $7.55 + $0.38/lb above first lb |
Source: 2026 US FBA fulfillment fee changes, Amazon Seller Central (US), data checked 2026-09-26. The full card, including Extra-Large and apparel rows, is on that page.
Three reading rules keep this line honest:
- Use the billable weight, not the product weight. Amazon’s page says fees for Large standard, Small Bulky, Large Bulky, and Extra-Large units are “based on the greater of unit weight or dimensional weight,” while small standard uses unit weight only (data checked 2026-09-26). Our dimensional weight guide shows the calculation, and FBA size tiers shows where the tier boundaries fall.
- Check the price band. A $9.99 item and a $10.00 item in the same tier pay different fees. Amazon states that products under $10 “automatically receive Low-Price FBA rates that are $0.86 less than standard FBA rates on average” (data checked 2026-09-26).
- Run a second pass for the holiday window. Amazon’s page states that “holiday peak fulfillment fees will apply from October 15, 2026 to January 14, 2027,” with the surcharge applying to those fees too (data checked 2026-09-26). A product whose break-even is close in September can flip in Q4.
Step 2: Price the FBM Side With the Same Discipline
The FBM side is where most homemade comparisons go wrong, because the costs are yours and nobody sends you an invoice for your own time.
- Postage. Price the label at the weight and zone mix you actually ship, not your cheapest zone. If you buy labels through Amazon Buy Shipping or a label platform, our Amazon shipping cost calculator comparison covers which tools quote FBM postage.
- Packaging and labor. Box, mailer, void fill, label stock, plus minutes per order times what an hour of your time (or a packer’s) costs. Even a two-minute pack at $18 an hour is $0.60 per unit.
- Your storage. Monthly rent or 3PL fee divided by units shipped per month. A spare room you already pay for is not free if it could hold faster-moving stock.
- Returns handling. Your category return rate times what it costs you to receive, inspect, and relist one unit.
On the FBA side, storage per unit is cubic feet per unit × monthly rate × months the unit sits, using the same holding period as your FBM storage. Amazon’s Monthly inventory storage fees page lists an off-peak (January–September) base rate of $0.78 per cubic foot for standard-size and $0.56 for oversize non-dangerous goods, rising to $2.40 and $1.40 in the October–December peak (data checked 2026-09-26). Our FBA storage fees guide covers the utilization surcharge that stacks on top.
Step 3: Three Products Through the FBA vs FBM Calculator
The fee lines below are Amazon’s published 2026 non-peak rates, checked 2026-09-26. Every other number — postage, labor, storage months, cubic feet — is an assumption for the example; swap in your own.
The products (assumed):
- A. A 12 oz phone accessory priced at $19.99, small standard, 0.05 cubic feet, two months of cover.
- B. A 2.2 lb kitchen gadget priced at $34.99, large standard, 0.25 cubic feet, two months of cover.
- C. A 12 lb (billable) folding step stool priced at $59.99, Small Bulky, 1.5 cubic feet, two months of cover, stored at Amazon’s $0.56 per cubic foot oversize off-peak rate.
| Line (per unit) | A | B | C |
|---|---|---|---|
| FBA fulfillment fee (rate card) | $3.78 | $5.92 | $7.55 + 11 × $0.38 = $11.73 |
| × 1.035 surcharge | $3.91 | $6.13 | $12.14 |
| FBA storage (cu ft × rate × 2 months) | $0.08 | $0.39 | $1.68 |
| Inbound placement and prep (assumed) | $0.20 | $0.35 | $0.90 |
| FBA cost per unit | $4.19 | $6.87 | $14.72 |
| FBM packaging and labor (assumed) | $0.60 | $0.90 | $1.80 |
| FBM own storage (assumed) | $0.03 | $0.10 | $0.40 |
| Break-even postage | $3.56 | $5.87 | $12.52 |
| Your actual postage (assumed) | $4.10 | $7.40 | $11.50 |
| FBM cost per unit | $4.73 | $8.40 | $13.70 |
| Cheaper method, per unit | FBA by $0.54 | FBA by $1.53 | FBM by $1.02 |
Returns handling is left at zero in this example to keep the table readable; in apparel or electronics it belongs on both sides.
The small and mid-weight items clear FBA; the bulky item tips toward FBM. The table adds what a rule of thumb cannot: the exact label price at which each answer changes.
The second check: does Prime lift overturn the saving?
Product C is $1.02 cheaper per unit through FBM, but the FBA listing carries the Prime badge and the FBM one does not (unless you qualify for Seller Fulfilled Prime). If FBA sells more units, it can win on total profit while losing per unit.
Break-even sales lift = per-unit FBM saving ÷ FBA profit per unit
Assume Product C makes $14.00 per unit profit under FBM after cost of goods, referral, and ads. Under FBA it makes $14.00 − $1.02 = $12.98. The break-even lift is $1.02 ÷ $12.98 = 7.9%. If FBA sells more than 7.9% more units than FBM would, FBA earns more in total; below that, FBM does.
Estimate the lift from your own history (an FBM period against an FBA period on the same ASIN), not a generic figure; it varies heavily by category.
Where the Referral Fee Stops Cancelling Out
The referral fee drops out of the comparison only when the price and the fee base are identical on both sides. Three cases break that:
- You charge shipping separately on FBM. Amazon’s pricing page states that “an item’s total price includes its list price, as well as shipping costs and any gift-wrapping charges,” and the referral percentage applies to that total (data checked 2026-09-26). A $19.99 item with $4.99 shipping pays referral on $24.98. Add that extra referral to the FBM side. Our referral fee guide has the category table and the calculation.
- The shipping charge pushes the total over a category threshold. In Beauty, Health and Personal Care, Amazon’s pricing page lists 8% for a total sales price of $10.00 or less and 15% above (data checked 2026-09-26). An $8.99 item with $2.99 shipping crosses into 15% on the whole total.
- You price the FBA and FBM offers differently. If you raise the FBM price to recover postage, the referral fee rises with it, and conversion usually falls. Compare total profit, not fee lines.
When to Hand It to a Third-Party Calculator
The hand formula is best when you are screening a product before you have an ASIN, or when you want to see which single input (label price, cubic feet, months of cover) moves the answer. For a live ASIN, a calculator is faster and removes transcription errors on the fee line.
- Amazon’s FBA Revenue Calculator is built for this comparison: Amazon’s pricing page says you can use it “to compare estimates for FBA and your own fulfillment method” (data checked 2026-09-26), so it is the fastest check on the fee lines. Our guide to reading the Revenue Calculator lists which costs it leaves out — the same inbound, returns, and ad lines this formula forces you to fill in.
- Free third-party calculators vary in what they model. SellerApp’s free calculator offers a side-by-side FBA vs FBM view, and the others cover different subsets of storage, returns, and advertising; the free FBA fee calculator roundup compares their coverage line by line (data checked 2026-07-19).
Whichever tool you use, run the break-even formula once by hand per product. It tells you which input the tool’s answer depends on, and that is the number to double-check.
Common Mistakes in FBA vs FBM Math
- Reading the rate card without the 3.5% surcharge. On Product C that alone is $0.41 per unit.
- Using product weight instead of billable weight. A light but boxy item can price one or more weight rows higher on FBA.
- Comparing FBA storage for one month against a year of FBM rent. Use the same months of cover on both sides.
- Treating your own time as free. FBM labor that you do yourself still has a cost, and it caps how far the FBM side can scale.
Frequently Asked Questions
How do you calculate FBA vs FBM break-even?
Add the FBA fulfillment fee (including the 3.5% surcharge in 2026), FBA storage per unit, and inbound placement and prep per unit. Subtract your own FBM packaging, labor, storage, and returns handling per unit. The result is the break-even postage: if your real shipping label costs less, FBM is cheaper per unit for that product.
Does the referral fee change between FBA and FBM?
Not at the same price in the same category. Amazon charges the same referral rate either way, so it cancels out of the comparison. It changes when you charge FBM shipping separately, because the referral fee applies to the total sales price including shipping.
Is FBM cheaper for heavy or bulky items?
Often, because bulky FBA fees climb with every pound and storage is billed by cubic foot. In the worked example above, a 12 lb Small Bulky item came out $1.02 per unit cheaper through FBM at an assumed $11.50 label; your real postage decides it.
Conclusion
An FBA vs FBM calculator comes down to one subtraction per SKU: Amazon’s all-in fulfillment cost minus your own non-postage costs is the most you can pay for a label and still come out ahead on FBM. Apply the 3.5% surcharge, use billable weight and the right price band, then check whether Prime lift covers the gap. Decide per product, as the FBA vs FBM guide recommends.
FBA fulfillment fee rates, the 3.5% surcharge, low-price rates, and peak dates checked 2026-09-26 against Amazon Seller Central’s 2026 US FBA fulfillment fee page. Storage rates checked 2026-09-26 against Amazon’s Monthly inventory storage fees page. Referral rates and the total-sales-price definition checked 2026-09-26 against sell.amazon.com/pricing. All other figures in the worked example are assumptions.