This is what happens when you use FineMargins. Read the steps or expand any section for the full technical detail.
Pick your platforms — Amazon, eBay, Walmart, Shopify, any combination. Enter your products: price, weight, category, how you ship it. Five minutes per product. Upload a CSV if you have more than a few.
Start with the basics — that's enough for the full published-fee analysis. Add COGS, ad spend, shipping costs, and return rates when you have them. Each one unlocks a deeper layer. Your dashboard shows exactly what you've provided and what more data would add:
"You've filled 18 of 23 cost lines. Adding your ad spend unlocks your break-even ACoS and promotional headroom."
14-day free trial. Takes 30 seconds to start.
Every product gets a full cost breakdown — every fee by name, using the platform's own terminology. Not two lines. Not "about 15%." Every fee between the sale price and your bank account.
Click any number. See how it was calculated — what variables drive it, what rate card it comes from. Click again for the source page and the date we last verified it. Three layers of depth. Go as deep as you want.
Alongside the breakdown: your break-even price, your maximum ad spend before the product loses money, and your contribution margin per unit. Each one explained. Each one drillable.
| Gross revenue | $34.99 |
| Referral fee (17%) | −$5.95 |
| FBA fulfilment + 3.5% fuel | −$4.66 |
| Storage (1 month) | −$0.07 |
| True net margin | $6.66 · 19.0% |
Illustrative dashboard. In the platform, every line is computed for your product.
Your fee calculator shows two lines on a $34.99 Running Shirt:
| Referral fee (15%) | $5.25 |
| FBA fulfilment | $3.95 |
| Total fees | $9.20 |
Three things are wrong.
The referral rate for Clothing and Accessories isn't 15%. It's 17% on items over $20 — a marginal rate structure published in the Amazon Referral Fee Schedule (✓ category_reference Row 13, verified 2026-04-18). Your $34.99 shirt pays $5.95 in referral, not $5.25.
The FBA fulfilment fee isn't $3.95. That's the non-apparel rate. Apparel has its own FBA rate schedule. Your shirt pays $4.50 (✓ fee_database Row 366, verified 2026-04-18).
And there's a third line your calculator doesn't show: a 3.5% fuel and logistics surcharge on every FBA fulfilment fee (✓ fee_rules Row 7, verified 2026-04-18). That's $0.16 per unit.
| What's wrong | Your calculator | Actual | Error |
|---|---|---|---|
| Referral rate | 15% flat ($5.25) | 17% banded ($5.95) | +$0.70/unit |
| FBA schedule | non-apparel ($3.95) | apparel ($4.50) | +$0.55/unit |
| Fuel surcharge | not included ($0.00) | 3.5% ($0.16) | +$0.16/unit |
| Total | $9.20 | $10.61 | +$1.41/unit |
Your real platform fees are $10.61 — not $9.20. At 1,000 units/month, that's $16,920/year in fees you aren't tracking.
Your calculator shows 2 lines. Here's the Running Shirt with every cost between the customer's payment and what actually lands in your bank account.
Zone 1: Platform Fees (verified from published rate schedules)
| # | Description | Amount | Status | Source |
|---|---|---|---|---|
| 1 | Gross Revenue | $34.99 | — | Product listing price |
| 2 | (−) Referral Fee (17%) | $5.95 | ✓ | category_reference Row 13, verified 2026-04-18 |
| 3 | (−) Listing Fee | $0.00 | ✓ | Professional plan — no per-item fee |
| 4 | (−) Subscription | $39.99/mo | ✓ | Row 1213 (account-level, not per-unit) |
| 5 | = Net Revenue After Platform Fees | $29.04 |
Zone 2: Fulfilment & Product Cost
| # | Description | Amount | Status | Source |
|---|---|---|---|---|
| 6 | (−) FBA Fulfilment + 3.5% fuel | $4.66 | ✓ | Row 366 (apparel) + fee_rules Row 7 |
| 7 | (−) Storage (1 month, off-peak) | $0.07 | ⟷ | Row 920 ($0.78/cu ft) × 0.094 cu ft × 1 mo |
| 8 | (−) Pick & Pack | $0.00 | ✓ | Included in FBA fee |
| 9 | (−) Outbound Shipping | $0.00 | ✓ | Included in FBA fee |
| 10 | (−) Inbound Shipping | $2.50 | ⚠ | Illustrative — yours replaces this |
| 11 | = Gross Margin After Fulfilment | $21.81 | ||
| 12 | (−) COGS | $10.00 | ⚠ | Illustrative — yours replaces this |
| 13 | (−) FX on COGS | $0.00 | — | N/A for domestic sourcing |
| 14 | = Gross Profit | $11.81 |
Zone 3: Operating Costs & True Margin
| # | Description | Amount | Status | Source |
|---|---|---|---|---|
| 15 | (−) Advertising (12% ACoS) | $4.20 | ⚠ | Illustrative — yours replaces this |
| 16 | (−) Return Cost (15% rate) | $0.77 | ⚠ | Rate illustrative. Returns processing ✓ Row 943 |
| 17 | (−) Payment Processing | $0.00 | ✓ | Amazon handles payment processing |
| 18 | (−) FX on Revenue | $0.00 | — | N/A for US domestic seller |
| 19 | (−) Refund Admin | $0.18 | ⟷ | ✓ Row 1198 × ⚠ 15% return rate |
| 20 | = True Net Margin | $6.66 | ||
| 21 | = True Net Margin % | 19.0% |
The $25.79 your calculator showed? After every real cost, you keep $6.66.
Colour key: ✓ = from published rate card, source linked. ⟷ = computed from verified rates + product attributes. ⚠ = illustrative — in the platform, your real number replaces this.
Change your COGS from $10.00 to $8.00 and every number below Line 12 recalculates. Your True Net Margin moves from $6.66 to $8.66 — a 30% improvement from a $2.00 sourcing change. The waterfall shows you exactly where that $2.00 flows.
The breakdown is the starting point. Here's what comes next.
Fees you didn't know about. Surcharges not on the rate card page. Costs your current tools don't track. Each one flagged with the source link and what it's costing you per year.
Programmes you qualify for. Certifications that remove surcharges. Discount tiers you've crossed without knowing. Enrolments that lapsed. Each one with the annual value and what it takes to claim it.
What happens if you change something. Switch fulfilment method, change your price, try a different platform — one change, every connected cost updates. See the full impact before you commit.
What your product would cost somewhere else. Run the same product on a different platform. See the comparison with real numbers — not headline rates, the full fee structure including the costs the other platform doesn't have. See a real comparison →
Your Yoga Mat ($39.99, Small Bulky) pays a $1.51/unit packaging surcharge because you're not enrolled in SIPP. Free certification. No trade-off. Here's what changes:
| Metric | Before SIPP | After SIPP | Change |
|---|---|---|---|
| Packaging surcharge | $1.51/unit | $0.00/unit | −$1.51 |
| True Net Margin | $1.96 (4.9%) | $3.47 (8.7%) | +$1.51 |
| Break-even ACoS | 14.9% | 18.7% | +3.8 pp |
| Annual saving (1,200 units) | — | $1,812/year | Free |
One input changed. Four metrics moved. The break-even ACoS widened by 3.8 percentage points — meaning you can spend significantly more on advertising before this product loses money.
On the Running Shirt (apparel, Large standard), the same SIPP enrolment saves $0.06/unit — small. The cascade mechanics are identical. The magnitude depends on the product. That's why it runs on every product in your catalogue.
Same product. Two platforms. The gap is $4.75/unit — and it's almost entirely fulfilment.
| Amazon (FBA) | Walmart (WFS) | |
|---|---|---|
| Referral | $6.00 | $6.00 |
| Fulfilment | $9.07 + $1.51 + $0.32 | $6.15 |
| Zone 1 | $16.90 | $12.15 |
| Annual gap (2,400 units) | $11,400 cheaper on Walmart |
And Walmart has no fuel surcharge, no per-item subscription fee, and no packaging penalty. Three cost lines that exist on Amazon and are absent on Walmart.
With New-Seller Savings (20% off referral), Walmart drops further to $10.95. $14,280/year cheaper.
Amazon updated 247 FBA rate cells in January 2026. Most sellers found out three months later when their margins showed it.
Your analysis updates automatically when a rate card changes. You see the impact on the day it hits — not in the quarterly review. Programme eligibility, policy updates, new alternatives — each one checked against your products, each month, without you doing anything.
A one-time calculation is a snapshot of a moving target.
The waterfall isn't just a cost breakdown. It's the input to every business decision.
Break-even ACoS: 31.0% (Running Shirt)
Your advertising can consume up to 31.0% of revenue before this product loses money. Most sellers calculate break-even ACoS from revenue minus referral fee minus FBA. That gives 69.8% — more than double the real number. They scale advertising past the true break-even point without knowing it.
Promotional headroom: 19.0%
You can discount this product up to 19.0% before True Net Margin hits zero. That's a maximum Prime Day discount of $6.65 off $34.99 before you're selling at a loss. Every cost reduction from the steps above widens this window.
These numbers recalculate when anything changes. A rate card update. A new programme enrolment. A sourcing change. The waterfall is the foundation — change any cost line and the break-even, headroom, and contribution margin all update instantly.
Why a subscription: rate cards change quarterly. FineMargins monitors 1,257 source URLs. When a rate changes, your portfolio re-analyses automatically. After setup, you open it and the work is done.
Everything above runs on every product in your catalogue. When you have multiple products, new patterns emerge that single-product analysis can't show.
Download your full analysis as a per-platform CSV. Every column uses the same fee names you see in your settlement reports — Referral Fee on Amazon, Final Value Fee on eBay, Transaction Fee on Shopify. No translation needed.
The export includes numbers no other tool computes:
Floor prices — the minimum price where you still make your target margin, accounting for every platform fee. Your repricer needs this number. Right now you're guessing it.
ACoS ceilings — the maximum advertising cost of sale before your product loses money. Your PPC tool needs this number. Right now you're guessing it.
Fee verification — every fee individually calculated from published rate schedules with verification dates. Open it next to your settlement report and check every line yourself.
One file. Every product. Every fee. Ready to use in whatever tool you already run your business with.
Five products. Four categories. Your calculator says all are profitable. The full analysis says one is barely surviving at 4.9% margin.
| Product | Price | Calculator margin | True Net Margin | True Net $/unit |
|---|---|---|---|---|
| Running Shirt | $34.99 | ~$25.79 | 19.0% | $6.66 |
| Wireless Earbuds | $49.99 | ~$42.04 | 33.4% | $16.68 |
| Vitamin D | $18.99 | ~$12.14 | 13.2% | $2.51 |
| Phone Case | $12.99 | ~$7.62 | 15.9% | $2.06 |
| Yoga Mat | $39.99 | ~$23.99 | 4.9% | $1.96 |
Revenue contribution ≠ profit contribution. The Earbuds contribute 24% of revenue but 38% of profit. The Yoga Mat contributes 13% of revenue but under 3% of profit. One product is carrying the portfolio. Another is dead weight.
| Product | Break-even ACoS | Illustrative ACoS | Headroom |
|---|---|---|---|
| Earbuds | 41.4% | 8% | 33.4 pp |
| Running Shirt | 31.0% | 12% | 19.0 pp |
| Vitamin D | 28.2% | 15% | 13.2 pp |
| Phone Case | 25.9% | 10% | 15.9 pp |
| Yoga Mat | 14.9% | 10% | 4.9 pp |
Running the same 15% ACoS target across all five means the Yoga Mat is already past break-even — losing $0.04 per unit. The Earbuds have 26.4 points of unused runway.
The Yoga Mat is losing money at your uniform ACoS target. If ACoS drifts to 18% — realistic for competitive Sports & Outdoors keywords — it loses $1.24/unit. At 100 units/month, that's $1,488/year in losses on a product that was never profitable at your target.
Referral rates range from 8% to 17% across this portfolio. The Earbuds (Consumer Electronics, 8%) generate more profit per unit than the Running Shirt (Clothing & Accessories, 17%) despite lower volume — because the referral rate difference compounds through every line.
Referral rates are non-negotiable. But knowing that your 8% category product generates more margin per dollar of effort than your 17% category product changes where you allocate time, advertising budget, and inventory investment.
One product carries 77% of its margin as a penalty from a single programme non-enrolment (the Yoga Mat's SIPP surcharge). Two products have True Net Margin below 15%. The analysis surfaces which products are fragile and where one fee change would push them negative.
The analysis runs each marketplace from its own published rate cards. Not one estimated from another. Not a currency conversion applied to US rates.
Multiple regions — the same product costs different amounts on different Amazon marketplaces. UK FBA rates, EU surcharges, Digital Services Tax by seller establishment — each marketplace has its own fee structure. How fees differ across 26 marketplaces →
Multiple platforms — the same product across Amazon, eBay, Walmart, and Shopify. Not a headline comparison — the full fee structure, including costs that only exist on one platform. Amazon vs eBay → · Amazon vs Walmart → · Amazon vs Shopify → · eBay vs Shopify → · Amazon UK vs US vs EU →
Every number links to a published source. Every analysis is reproducible. Database: 8,938 fee records, 1,257 source URLs, 1,652 things you can change, 1,705 programme eligibility rules.
Every number on this site comes from one of two places: a published platform page, or an estimate we made for the demonstration. We never mix the two without telling you.
When Amazon publishes a fulfilment rate, we extract that rate. We link to the page. We date the extraction. You can click through, read the page, and check the number matches. If it doesn't — because the platform updated the page and we haven't caught it yet, or because your product triggers a different band — tell us. We'll fix it or explain the difference.
We don't infer across marketplaces. Amazon UK's FBA rate is extracted from Amazon UK's fee schedule, not derived from the US rate with a currency conversion. We don't average, substitute, or fill gaps. If a platform publishes it, we mirror it. If they don't, we don't make one up.
For the demonstrations on this site, we need numbers the platform would normally collect from you — what you pay for goods, what you spend on advertising, how you ship to the warehouse. We don't have your numbers, so we estimate. Every estimate is labelled and includes the reasoning: a $34.99 polyester running shirt at mid-range retail typically lands at 25–35% COGS, so we estimate $10.00 (28.6%). You can judge whether our estimate is close to your reality.
When you use the platform, your numbers replace ours. The computation stays the same. The inputs become real.
Some inputs you might not have to hand — your return rate, your inbound shipping cost, your storage duration. The platform doesn't stop. It uses a category-based default and tells you exactly what it assumed, why, and what the impact range looks like. "This margin assumes a return rate of 8% — the category average for Health & Personal Care. At 15% returns, this margin drops from 42% to 36%. Provide your actual return rate for a corrected figure."
You get a working analysis immediately. When you have the real number, you put it in and the output updates. The default is a starting point with reasoning, not a guess without context. And it's always flagged — the platform never lets a default look like a verified input.
Some costs are quoted, negotiated, or vary by seller in ways no default can represent responsibly. Payment service provider rates. Freight forwarder quotes. Insurance premiums. When a cost falls in this category, we don't invent a number. We tell you the cost exists, show you where it sits in your waterfall, and tell you what we need from you to compute it. Not a generic "provide more data" — a specific "Provide your PSP rate to compute Line 17: Payment Processing Fee."
Every tool shows you a number. This is the only one that shows you the number, the calculation, the source page, and a named list of what the number does NOT include.