A 2.6% rate sounds small until you multiply it by a year of sales. Enter your monthly card volume and your average ticket, and this calculator shows what you actually pay each month under flat-rate pricing, Square online, Stripe online, and interchange-plus — side by side, with the effective rate most fee quotes never show you.
Estimates only, using the published 2026 US rates shown in the model list. Interchange is not one fixed rate: it varies by card type, rewards tier and how the card is taken, so the interchange-plus result moves with the average you enter. Monthly account fees, hardware, chargebacks and refunds are not included.
Flat rate vs interchange-plus, in plain terms
Flat-rate processors charge one blended percentage plus a small fixed fee on every sale, whatever card the customer used. It is predictable, and for small volumes it is usually the cheapest simple option — but you pay the same rate on a cheap debit card as on a premium rewards credit card. Interchange-plus separates the bill: you pay the card networks’ interchange rate (which varies by card) plus your processor’s fixed markup. On the default example in this calculator — $10,000 a month at a $50 average ticket — flat rate at 2.6% plus $0.15 costs $290.00 a month, an effective rate of 2.90%. Square online at 3.3% plus $0.30 costs $390.00. Stripe online at 2.9% plus $0.30 costs $350.00. Interchange-plus at a 1.8% average interchange plus a 0.30% markup and $0.10 per transaction costs $230.00. The gap between the most and least expensive model is $160 a month — $1,920 a year — on the same sales.
Why your average ticket changes everything
The fixed per-transaction fee is why ticket size matters. At a $50 average ticket, a $0.30 fee adds 0.6% to your real rate. At a $10 ticket, the same fee adds 3% — more than the headline percentage itself. Low-ticket businesses should obsess over the cents figure; high-ticket businesses should obsess over the percentage. For the full published rate tables behind the Square and Stripe models in this calculator, see our guide to how much Square charges per transaction.
Frequently asked questions
What is a normal effective rate for a small business? Most small businesses land between 2.5% and 3.5% once the fixed fees are counted. If your effective rate is above that, your ticket size, your card mix or your pricing model is working against you. When does interchange-plus beat flat rate? Usually as volume grows and average tickets rise, because the markup is smaller than the margin built into blended flat rates — but it depends on your card mix, which is why this calculator lets you test your own average interchange. Are these fees the whole cost? No. Monthly account fees, hardware, chargebacks, refunds and instant-transfer fees sit on top; this calculator covers the per-transaction cost, which is the part that scales with every sale.