About Seller Sum

Seller Sum is free fee and profit calculators for online sellers: eBay, Etsy, PayPal, Stripe, Square and more. It exists because the most-used fee calculators on the web run on stale numbers, some unchanged since 2022.

Who runs this

One person: the owner of a cross-border print e-commerce business, a cloud cost specialist by trade. I build these calculators because I use them. Fees come off my own margins every week, in two countries, so the numbers here get checked like my money depends on it. It does.

How the numbers stay right

• One source of truth. Every rate lives in a single versioned data file with the official source URL and a verbatim quote from it. Calculators, fee tables and the changelog all render from that file, so they can't disagree.
• Tested against the marketplaces' own examples. Where a platform publishes worked examples (eBay does), our test suite reproduces them to the cent. Where they don't, tests assert the exact published rate text. A fee update that breaks a test doesn't ship.
• Dated, visibly. Every page shows when its numbers were last verified against the official source, and the changelog records what changed and when.

How this site makes money

Some pages recommend tools through affiliate links (always disclosed in-place). We may add unobtrusive ads later. Neither changes the numbers: rates come from the marketplaces' official pages, quoted and dated, whether or not there's a commission anywhere near them.

Found a discrepancy? The fee pages change quietly and we'd rather hear it twice than miss it once. Check the changelog for the current verification dates.