How FeeTrail calculates seller profit

Completed-sale profit

Seller revenue is item price plus shipping income. Net payout subtracts marketplace and payment fees. Completed-sale profit then subtracts item cost, actual shipping, packaging and other direct costs.

Margin is completed-sale profit divided by seller revenue. ROI is completed-sale profit divided by invested item and fulfilment cost. Effective seller fee rate is seller-paid fees divided by seller revenue. Buyer-paid fees never enter seller deductions twice.

Money and rounding

Amounts are stored as integer minor units—cents for USD and pence for GBP. Each fee rule defines its base and rounds at its own calculation point.

Reverse decisions

Target price uses a monotonic search to find the lowest cent that meets the target, including threshold and fixed-fee changes. Max buy cost uses the same forward result as its source of truth.

Risk-adjusted expected profit

Expected profit weights the completed-sale and return scenarios by the user-entered return probability. A return scenario can include return postage, lost item value and fees the platform does not refund. It is a planning expectation, not a prediction.

Source priority and tax scope

FeeTrail prioritises current platform pricing, seller-help and legal pages over secondary explanations. Rules record the source, retrieval date, effective period and a content hash. Buyer sales tax or VAT is included only when the fee base requires it; income, corporation and personal tax are excluded. Recoverability of fee VAT is not tax advice.

Comparison limits

“Highest profit” describes only the entered scenario. Audience, likelihood and speed of a sale, customer support, returns policy and operational effort can outweigh the displayed fee difference.

Updates, corrections and rollback

A changed source is reviewed before a new version is published and tested against hand calculations. Platform changes and FeeTrail corrections receive different labels. An old receipt keeps its original schedule snapshot; recalculation creates a second receipt. If a release is wrong, the affected version is removed from current selection, the last tested schedule is restored, and the correction is recorded in Fee updates.

The V1 maintenance runbook includes source-check, registry, golden-test, build and browser gates. Its recorded rollback drill injects an isolated plausible fee defect, detects the changed golden result, restores the published selector and proves the original receipt is immutable.