Flat Rate vs Interchange-Plus: Where the Crossover Actually Is
The same $25,000 a month priced seven ways, and the volume at which switching starts paying.
The two models
Flat rate (Square, Stripe, Shopify, Toast) charges one published percentage plus a few cents, whatever the card. Simple, no monthly fee, no negotiation. Interchange-plus (Helcim, Stax, most merchant accounts) passes through the card network's own cost and adds a fixed margin. Cheaper at volume, and harder to compare.
Our basket, priced
$25,000 a month, 900 transactions, $28 average, all card-present: Helcim $658, Stripe $720, Clover $770, Square $785, Toast $787, Shopify $794, Lightspeed $860. Software and monthly fees are included; hardware is not.
Where the crossover sits
Below about $10,000 a month, flat rate almost always wins because interchange-plus providers add a monthly fee that a small volume cannot absorb. Between $10,000 and $25,000 it depends on your card mix — lots of rewards and business cards push interchange up and favour flat rate. Above $25,000, interchange-plus is usually cheaper, and by $50,000 the gap is worth a few hundred dollars a month.
What to ask before signing
- The full rate including every per-transaction fee, in writing.
- Every monthly charge: software, gateway, PCI, statement, minimum.
- Contract length and the early-termination fee.
- Who owns the hardware and whether it is locked to this processor.
- Under what circumstances funds can be held.
A provider that will not answer all five in writing before you sign has told you something.
» See the full rankings: Best POS Systems for Small Business in 2026, Cheapest Card Processing for Small Business, Best Free POS Systems .