Flat-rate processing, explained
Stripe and Square are flat-rate processors: they charge a percentage plus a fixed fee on every successful card payment, with no monthly fee or minimum on a standard account. Stripe’s standard U.S. rate is 2.9% plus $0.30 per charge, with extra charges for international cards and currency conversion. Square’s published rates are 2.6% plus $0.10 for in-person payments and 2.9% plus $0.30 online. The Shopify calculator adds the cost of selling through a Shopify store, and the credit-card processing calculator applies a percentage and a per-transaction fee that you enter.
In person or online
Where the customer is matters. In-person payments are usually cheaper to process than online ones, which is why the Square calculator separates them. If you sell in both places, run both numbers. A small difference in rate matters more as your volume grows, so compare using your real monthly sales.
When rates go lower
Larger sellers can negotiate custom pricing, and interchange-plus pricing through a dedicated processor can beat a flat rate at high volume if you know your card mix. The processor finder can point you in the right direction, and each calculator shows your own numbers before you commit.
Choosing between them
If most of your sales happen at a counter or market stall, start with the Square calculator. If you sell online or build your own checkout, start with Stripe. If you sell through a store platform, the Shopify calculator adds the platform’s own charges to the processing fee. Whatever you choose, enter your average sale amount and monthly volume, since the fixed part of the fee matters most on small sales.