The single biggest fee decision a growing business makes is whether to stay on simple flat-rate pricing or switch to interchange-plus. Here is how to know.
The three layers of every card fee
Every card transaction has three cost components:
| Layer | Who sets it | Who gets it |
|---|---|---|
| Interchange | Visa/Mastercard | The cardholder’s issuing bank |
| Scheme / assessment fees | Visa/Mastercard | The card network |
| Processor markup | Your processor | Your processor |
Flat-rate (Stripe, Square, PayPal) hides all three inside one number like 2.9% + $0.30. Interchange-plus (Adyen, Checkout.com, Helcim) shows interchange + scheme fees at cost, then adds a small, visible markup.
Why interchange-plus is cheaper at scale
A flat 2.9% bakes in a markup of roughly 0.9%-1% over typical interchange. An interchange-plus markup is often 0.2%-0.4%. On large volume that gap is real money:
| Monthly volume | Flat-rate (~2.9% + $0.30) | Interchange-plus (~2.2% effective) | Monthly saving |
|---|---|---|---|
| $5,000 | ~$165 | ~$130 | ~$35 |
| $25,000 | ~$800 | ~$575 | ~$225 |
| $100,000 | ~$3,200 | ~$2,300 | ~$900 |
(Illustrative; your real saving depends on card mix.) See the cheapest processors for high volume.
The crossover point
- Below ~$10k/mo: stay flat-rate. Simplicity wins and there is no monthly fee to amortize.
- $10k-$25k/mo: consider Helcim (interchange-plus, no monthly fee).
- Above ~$15k-$20k/mo: a Stax subscription (0% markup + monthly fee) often wins.
- Enterprise / global: Adyen and Checkout.com with local acquiring.
Read effective rate explained, then run your numbers in the calculator.