Fee methodology & sources

For any sale we first work out the gross: the item price plus whatever shipping you charge the buyer. Percentage fees that scale with the sale — final value, transaction, payment processing, regulatory operating, and cross-border fees — are applied to that gross amount. Where a platform’s percentage is banded — eBay’s final value fee, for example, is 13.6% on the portion of the sale up to $7,500 and 2.35% on the portion above it — each band is charged only on the part of the sale that falls inside it, so the effective rate drops on high-value sales. Where a platform charges its selling fee on the item price only (as Mercari and Grailed do), that is how we compute it, and the receipt line shows the exact base used. The promoted-listing / ad rate and any tiered commission (such as Poshmark’s) are applied to the item price, and minimum fees — such as Facebook Marketplace’s $0.40 floor — are enforced after the percentage is calculated.

Each fee is calculated and rounded to the cent on its own line, then the rounded lines are added up to get total fees. Rounding per component, rather than once at the end, mirrors how platforms post fees and stops tiny floating-point errors from stacking up. Net payout is gross minus total fees; profit is net payout minus your item cost and the shipping you actually pay.

The reverse solver(“price to net an amount”) works the formula backwards to estimate the list price that produces your target take-home, then checks the result against the real, rounded calculation and nudges it until the numbers agree to the cent.