How FBAbase calculates Amazon FBA profit

Last updated 21 August 2026

FBAbase combines seller-entered business costs with published formulas and, only where a page says so, dated Amazon US fee tables. The calculators estimate decisions such as per-unit profit, margin, ROI, fulfillment choice, and launch cash. They do not connect to Seller Central, import account transactions, reconcile settlements, or replace accounting and professional advice.

This page explains where each number comes from, how the calculations are checked, and how fee updates and corrections are handled.

Three types of numbers appear on FBAbase

The distinction matters. A precise result can still be wrong for a product when its inputs are incomplete or stale. Every calculator field ships on a demonstration value, labeled as such on the page, and is meant to be replaced with your own product-specific figures.

Core profit formulas

The Amazon FBA profit calculator uses this cost structure, and states the same formulas on the page itself:

Landed cost = supplier unit price + first-leg freight + prep & labeling

Referral fee = max(retail price × referral %, referral minimum)

Storage = unit volume × (off-peak months × off-peak rate + peak months × peak rate)

Cost of capital = landed cost × annual rate × days held ÷ 365

Holding cost = storage + aged-inventory surcharge + cost of capital

Operational cost = referral fee + FBA fulfillment fee + holding cost + advertising + return reserve + other Amazon fees

Net profit = retail price − landed cost − operational cost

Net margin = net profit ÷ retail price

ROI = net profit ÷ landed cost

Breakeven TACOS = profit before ad spend ÷ retail price

Blended TACOS = ACOS × ad-attributed share of sales

Breakeven ACOS = breakeven TACOS ÷ ad-attributed share of sales

Two details decide whether these produce the right answer. Every formula uses per-unit amounts unless the page names another unit, so a shipment total has to be divided across the sellable units before it enters per-unit profit - the calculator's freight helper does that division for you. And the aged-inventory surcharge is summed across the age bands a unit actually passes through, not charged at the top band for its whole life, which is the commonest way a spreadsheet overstates the cost of slow stock.

Calculator pages have different boundaries

FBAbase does not force one output label onto calculations with different scopes.

These boundaries prevent two common errors: calling after-fee proceeds complete profit, and treating a profitable unit as proof that the launch is affordable.

Fee-source policy

Four rules govern every fee claim on the site:

1. Amazon's own US pricing pages, Seller Central help, program documentation, or fee-change announcements are the primary source.
2. Any page carrying hardcoded fee data states its marketplace and its sourcing date. The rate cards currently in the fee calculator, the fee guide, and the homepage fee-lookup helper were sourced on 8 August 2026 for the US marketplace.
3. Seller-entered assumptions stay separate from published rate-table values. The main profit calculator ships no built-in fee table for exactly this reason: a hardcoded rate goes stale silently and the reader never finds out.
4. When a fee rule changes, the affected formula, worked example, page copy, and source link are all rechecked, not just the number.

A sourcing date means the displayed schedule was checked against the linked source on that date. It does not promise Amazon left the fee unchanged afterwards. Check the date, and confirm any material inventory decision in Seller Central. Third-party articles can help identify a question worth answering; they do not override Amazon's current fee documentation.

How a fee update is published

A fee update is complete only when every surface agrees:

• the calculator rate or lookup rule;
• the visible explanation and effective date;
• the worked example;
• the source link and sourcing date;
• the FAQ text and its matching structured data;
• the automated tests covering the changed boundary.

Changing the year in a title, or refreshing every date in the sitemap, verifies nothing. Pages that did not change keep truthful modification dates. Older examples are kept only when they are clearly labeled as historical; a current decision page uses the current verified schedule or asks you to enter the fee yourself.

How calculations and examples are checked

Every published worked example is reproducible from the page that owns the calculation. The review checks:

1. input units - per unit, per shipment, percentage, dollars, days, or monthly amount;
2. formula order and rounding;
3. fee minimums, price bands, size tiers, weight rules, and the other applicable branches;
4. exclusion boundaries, so a cost is neither missing nor counted twice;
5. the visible result against an independent manual calculation;
6. FAQ text and structured data for factual parity.

The calculation logic is covered by a unit-test suite that runs before every deploy, along with a check that each page's visible FAQ and its FAQPage structured data still match question for question. Displayed results round to cents or to one decimal place; tests use the unrounded value wherever rounding could move a threshold or flip a verdict.

Assumptions stay visible

Advertising cost, return rate, future sale price, sales lift, days held, and inventory turns usually begin as assumptions. A calculator can show the consequence of an assumption. It cannot prove the assumption will hold.

Corrections policy

A material formula, fee, example, or explanation is corrected as soon as the issue is verified, and each correction below states the date, the affected page and calculation, what was wrong, what changed, whether displayed results could have moved, and how the fix was verified.

Scheduled fee updates and factual corrections carry different labels. A new Amazon rate does not mean the old page was wrong when it was published. A formula or transcription error does.

To report a suspected error, use the contact details on the About page: [email protected] or @SukeJ56505 on X. The issue is reproduced before any result changes, and the correction note stays visible when the error could have affected a seller's decision.

Correction history

No further material corrections have been recorded as of 21 August 2026.

Who maintains FBAbase

FBAbase is maintained by a software developer, not presented as the work of a full-time Amazon seller, accountant, customs broker, or tax adviser. Credibility here comes from formulas you can read on the page, primary sources, dated checks, reproducible examples, stated limits, and corrections when the evidence changes. The About page explains why the tools were built and how to get in touch.

Privacy and data handling

Calculator inputs are processed in your browser. There is no Amazon login, no supplier-file upload, and no Seller Central API connection. Saved calculator records live in your browser's local storage until you clear them, and nobody, including us, can read them.

The site still makes ordinary network requests to load its pages. Cloudflare hosts FBAbase, and Cloudflare Web Analytics receives aggregate page-view and page-speed information. That service is cookieless and receives no calculator-field values, because those values are never written to the page's network traffic. The privacy policy carries the complete disclosure.

What FBAbase does not verify

• your product's future sale price, demand, or advertising performance;
• the accuracy of a supplier quote or a freight allocation across units;
• account-specific Seller Central charges you did not enter;
• customs classification, tax treatment, or legal compliance;
• whether inventory will sell before storage or aging costs increase.

Results are estimates for decisions, not guarantees and not financial statements. The terms set out the applicable limitations.

Primary reference starting points

• Amazon selling fees and referral-fee rules
• Amazon fee-estimation tools
• Fulfillment by Amazon overview
• Amazon Ads ACOS guide
• FBAbase: 2026 Amazon FBA fee sources and tables

Each fee-bearing page keeps its own marketplace, effective date, source links, and sourcing date. This page describes the policy behind them.