Fee Math: A calculator compares net payout for the same card across eBay, TCGPlayer, Whatnot and Cardmarket, including fees, shipping and currency conversion.

Build the four-fee comparison first, keep it free, and monetize with a Pro tier that stores your full flip ledger.

Why it can work: Fee structures differ by 10 to 20 percent of the sale price across marketplaces, so a payout calculator directly changes where and how sellers list.