Methodology

Methodology version: July 20, 2026

Where fee information comes from

Marketplace defaults come from publicly accessible official policies, seller help centers, pricing pages, and official seller announcements. A blog, search snippet, forum reply from an unidentified seller, or competing calculator can help locate a topic but is not accepted as fee authority.

Every stored rate records the marketplace, US region, USD currency, fee basis, source URL, last-verified date, explanation, thresholds, and any known minimum or maximum. The schedule has its own version so a rate update does not rewrite the calculation logic or erase the prior snapshot.

How often rates are reviewed

Our review standard is at least once every 90 days for published marketplace calculators, and sooner when an official announcement, seller report, or test discrepancy indicates a change. A last-verified date means the linked public source was checked on that date; it is not a guarantee that a marketplace has not changed a private or newly published rule since then.

Temporary programs receive extra caution. For example, Amazon describes the 2026 FBA surcharge as temporary, and Whatnot describes some high-value commission tiers as limited-time. Those conditions remain visible beside the calculator.

How an order is represented

The engine first separates buyer-facing gross order value from seller revenue. Buyer sales tax can be part of a marketplace fee basis, but it is not seller revenue. Buyer-paid shipping is treated according to the marketplace flow: it can be seller revenue on one platform and a platform-handled amount on another.

Each fee is calculated from its documented basis and rounded to cents for display. Estimated payout equals seller revenue minus fees deducted from proceeds. Net profit goes further by subtracting item cost, actual shipping, packaging, advertising, and miscellaneous seller costs. Margin is profit divided by seller revenue; ROI is profit divided by total cost.

How calculations are tested

Pure calculation functions are tested independently from the interface. The test suite covers every supported marketplace, fixed and percentage fees, whole-order and graduated tiers, thresholds, minimums, caps, category differences, overrides, malformed and extreme values, and official worked examples where the marketplace publishes one.

Reverse pricing is tested by taking the solved selling price and feeding it back through the forward calculator. Browser tests complete one user flow per calculator, preserve a product when moving into comparison, exercise Copy and Reset, inspect every public route, and fail on browser console errors.

Why an actual payout can differ

Differences can come from category classification, seller plan, package measurements, taxes on seller fees, currency conversion, advertising attribution, creator commission, promotions, refunds, reserves, chargebacks, fulfillment adjustments, inventory fees, seller-performance surcharges, or a policy change after the review date.

Product-specific values are never guessed. Amazon FBA fulfillment, for example, must be entered from Amazon's Revenue Calculator, fee preview, or current statement because dimensions, weight, price, and services affect the charge.

How to report an outdated fee

Email hello@sellertake.com or follow the correction-report checklist. Include the marketplace, seller country, category or plan, official source URL, effective date, the inputs used, and the fee line you expected. Remove names, addresses, order numbers, and other personal information from screenshots.

What a correction changes

A confirmed rate change creates a new fee-data version, updates visible verification and history entries, and adds or changes boundary tests. Calculation code changes only when the marketplace changes the mathematical behavior—not merely because a number changes.