Interchange-Plus vs Flat-Rate Processing: Where the Margin Hides

Card acceptance has three cost layers: interchange set by the card networks and paid to the issuing bank, network assessments, and the processor markup. Only the third layer is negotiable — and flat-rate pricing exists to keep you from seeing where it sits.

The two models

Flat rate bundles everything into one number, for example 2.9% plus a fixed per-transaction fee. Simple, predictable, and typically 40 to 90 basis points above cost on a card mix weighted toward debit.

Interchange-plus (IC++) passes through interchange and assessments at cost and adds a disclosed markup, quoted as basis points plus cents per transaction. It is harder to read and almost always cheaper above roughly 50,000 a month in volume.

Calculate your effective rate first

Take last month's statement: total fees divided by total card volume. That single percentage is your effective rate, and it is the only number worth comparing across quotes. Do it separately for card-present and card-not-present volume, because the interchange gap between them is large.

What to demand in a quote

• Markup expressed as basis points plus cents, with interchange passed through at cost.
• A written list of monthly fees: gateway, PCI, statement, batch, minimum-volume, and non-qualified surcharges.
• The contract term, early termination fee and auto-renewal clause. Three-year terms with liquidated-damages exits are still common.
• Reserve terms and payout timing — a rolling reserve of 5% held 90 days is a working-capital cost, not a fee.

Cost reduction that does not require switching

• Level 2 and Level 3 data on B2B card payments can cut interchange meaningfully on commercial cards; it requires sending tax amount, customer code and line-item detail.
• Account updater reduces failed recurring charges, which are more expensive than they look once retry fees and churn are counted.
• Routing debit over least-cost networks where regulation permits.

The negotiating leverage

Processors price against churn risk. A clean statement analysis, two competing IC++ quotes and a documented effective rate are worth more than a phone call about loyalty. Renegotiate annually; markups drift upward quietly.

General information for business readers, not a recommendation of any provider.