How card processing fees actually work
Every card sale gets a slice taken off the top before the money reaches your account. That slice is built from three parts: interchange (paid to your customer's bank), assessments (the card network's cut), and your processor's markup. Interchange and assessments are fixed for everyone; only the markup is negotiable.
Most processors quote that total as a percentage plus a fixed per-transaction fee — the two inputs above. A common US flat rate is 2.9% + $0.30 online. On a $40 sale that's $1.46; on a $5 sale it's $0.45 (9% of the sale, because the fixed 30 cents dominates small tickets). That's why your effective rate moves with your average ticket size.
Compare effective rates, not headline rates. Take one month's total fees (every line, not just the percentage) and divide by total card sales. That single number is the only fair way to compare two providers.
Flat-rate vs interchange-plus
Flat-rate (Stripe, Square, PayPal) charges one blended percentage on every card. It's simple and predictable, with no monthly fee — but you quietly overpay on cheap debit. Interchange-plus passes the real interchange through at cost and adds a fixed markup (e.g. interchange + 0.30% + $0.10). It's the most transparent model and usually the cheapest once you're doing real volume — interchange-plus typically starts winning around $4,000/month on Stripe, $7,500 on Square, and $10,000 on Clover.
Use the monthly volume field above to see your projected annual cost at the current effective rate — then compare it against an interchange-plus quote.
Frequently Asked Questions
How does this credit card processing fee calculator work?
Enter the sale amount and your rate as a percentage plus a fixed per-transaction fee (or tap a preset). The calculator multiplies the amount by the percentage, adds the fixed fee, and shows the total fee, your effective rate, and what you keep — plus an optional monthly projection.
What rate should I enter?
Use your processor's published rate. Common US flat rates are 2.9% + $0.30 online and 2.6% + $0.15 in person; on an interchange-plus plan, enter your blended effective percentage. If you are not sure, check a recent statement or one of the per-brand calculators linked below.
What is an effective rate?
It is your total fees divided by total card sales — the single number that folds the percentage, the fixed fee, and any add-ons together. It is the honest way to compare two processors, since the fixed fee makes small tickets cost a higher percentage.
Why does my effective rate change with the sale amount?
Because of the fixed per-transaction fee. At 2.9% + $0.30, a $100 sale costs 3.2% but a $5 sale costs 9% — the 30 cents is a big share of a small ticket. A larger average ticket pulls your effective rate down toward the percentage.
How do I get a lower processing rate?
Ask for interchange-plus pricing once you have steady volume, run more sales in person and on debit, send full card data (AVS/CVV) so payments qualify for cheaper interchange, and negotiate the processor markup. Our processing-fees guide has the full playbook.