Payment processing fees consist of two components: a percentage of the transaction plus a flat fee per transaction. Stripe's standard rate is 2.9% + $0.30 for US domestic cards. This means on a $100 sale, you pay $2.90 (percentage) + $0.30 (flat fee) = $3.20 total, netting you $96.80. The flat fee becomes proportionally more expensive for low-price products — on a $10 sale, that $0.30 represents 3% of the transaction, bringing your effective rate to 5.9%.
Why the percentage model exists: Card networks (Visa, Mastercard) and issuing banks take a cut of every transaction as "interchange fees." Payment processors like Stripe add their own margin on top. This system exists because credit card transactions involve risk (fraud, chargebacks) and infrastructure (secure processing, compliance, data handling). The processor is betting that legitimate transactions will outnumber fraudulent ones and provide enough margin to be profitable.
Volume discounts become available as your processing volume increases. Stripe's standard rate applies up to about $80,000/month in volume. Beyond that, you can negotiate custom pricing — often dropping to 2.4-2.6% + $0.30 for high-volume businesses. At $1M+/month, some businesses negotiate down to 1.9% + $0.20 or lower. However, these custom rates require direct relationships and typically yearly commitments. For most indie developers and small businesses, standard rates apply.
International fees add complexity. Cross-border transactions (selling from the US to a European customer) typically add 1-1.5% to your fee. Currency conversion adds another 1-2% depending on the provider. If you're selling globally, these fees compound quickly — a 2.9% + $0.30 transaction might become 4.4% + $0.30 for international sales. Some platforms like Paddle handle this better by becoming the merchant of record and dealing with local payment methods and tax compliance, though they charge higher base rates.
Hidden costs matter too: Some platforms charge for failed payments, subscription management, customer portal access, or advanced reporting. Stripe includes these features in the base pricing, but Paddle and FastSpring include tax handling and compliance in their higher rates. When comparing platforms, calculate total cost of ownership, not just transaction fees.