How we check fees
Every rate on this site comes from the platform's own fee page, carries the date we last checked it, and runs through a calculator that has been tested against a second, independent implementation of the same rules.
Where the numbers come from
We read each platform's own fee page: eBay's help pages, PayPal's merchant fees page, Stripe's pricing page, Venmo's fee page, Square's pricing page, and the help centres of Etsy, Depop, Mercari, Poshmark and Whatnot. We never copy rates from other calculators, blogs or forums.
Each calculator links its fee page next to the result and shows the date we last checked it. The rates are stored as data with that link and date attached, so a page cannot show a rate without its source.
How we check the maths
Every calculator has unit tests built from the platform's own worked examples and from hand-checked sales. Before a calculator goes live, a second implementation is written only from the platform's fee page, without looking at ours, and the two are compared on thousands of sales: every category or method, every band edge, rounding ties, costs that turn a sale into a loss, and the reverse 'price to ask' mode.
Any difference is treated as a bug until it is explained. Most differences turn out to be places where the fee page does not say what happens; we decide those openly, as listed below, and the comparison then has to pass in full.
When a fee page is unclear
Fee pages rarely say how they round or what happens at the edges. These are the readings we use everywhere:
- Each fee line is rounded to the nearest cent, half a cent upwards, before the lines are added.
- A minimum fee is never more than the payment it is taken from: a $1 minimum on a 50-cent payment charges 50 cents. Fixed per-payment fees, such as 30 cents on a card, apply in full, so a very small payment can show a loss.
- A sale of zero has no fees.
- Where a fee applies to 'the sale amount' without saying whether tax is included, we follow the platform's rule for its main fee (for example, Etsy's currency conversion fee leaves out US sales tax, like its transaction fee).
- Where a platform's table shows no cap, we show no cap, and say so (for example, ACH invoices on Square's Free plan).
How often we re-check
Every week an automated check compares each fee page with the week before and flags any change in its numbers. Once a month every rate is read again from the platform's page and its checked date updated. When a platform changes a fee, the calculator, its tests and its independent check are updated together before the new rate goes live.
Found a number that looks wrong?
Every result has a 'Number looks wrong? Tell us' link. It opens an email with the calculation link and the date we checked the rates; paste what the platform actually charged. We re-check the platform's page and, if we were wrong, fix the data and add the case to the tests.
Your entries never leave your browser unless you send that email yourself.