Flat-Rate vs. Interchange-Plus: Which Payment Processing Pricing Model Saves You More?

If you take card payments, you've probably seen both terms thrown around by payment processors: flat-rate and interchange-plus. They sound like technical jargon, but the difference between them can add up to real money over a year of transactions — sometimes thousands of dollars for a growing business. This guide breaks down exactly how each model works, who each one is built for, and how to figure out which one actually costs you less.

What is flat-rate pricing?

Flat-rate pricing is exactly what it sounds like: one all-in percentage plus a small fixed fee, charged on every card transaction regardless of the card type, the customer's bank, or how the transaction was processed. A typical flat rate looks like 2.6% + 10¢ per transaction. That means a $100 sale costs you $2.70 in processing fees, whether the customer paid with a rewards credit card, a basic debit card, or an American Express card that would otherwise carry a higher underlying cost.

The processor absorbs the variability between different card types and networks, and in exchange, they build in a margin that covers the average cost across all the cards they see. For merchants, the appeal is predictability: you can calculate your exact processing cost on any transaction without needing to understand interchange categories, network assessments, or card-brand fee schedules.

What is interchange-plus pricing?

Interchange-plus pricing (sometimes called "cost-plus" pricing) separates your processing cost into two visible parts: the interchange fee, which is set by the card networks (Visa, Mastercard, Discover, American Express) and paid to the customer's issuing bank, and a fixed markup that your processor adds on top as their fee for providing the service.

Interchange fees vary quite a bit — a basic debit card might carry an interchange fee under 0.5%, while a premium rewards credit card can run 2% or more. Under interchange-plus, you pay the actual interchange rate for each transaction, plus a consistent markup like 0.20% + 8¢. So a debit transaction might cost you 0.65% + 8¢ total, while a premium rewards card might cost 2.20% + 8¢ — the markup portion stays the same, but the interchange portion moves with the card type.

This model is more transparent because you can see exactly what you're paying the bank versus what you're paying your processor. It's also usually cheaper overall, because you're not paying an averaged rate that's padded to cover the processor's exposure to expensive card types.

Side-by-side: how the two models actually compare

Let's walk through a concrete example. Say you run a small retail shop processing $20,000 a month in card sales, with a typical mix of debit cards, standard credit cards, and a handful of rewards cards.

Flat-rate at 2.6% + 10¢

Assuming roughly 400 transactions averaging $50 each: 400 × $50 × 2.6% = $520, plus 400 × $0.10 = $40. Total monthly cost: $560.

Interchange-plus at interchange + 0.20% + 8¢

Assume your blended average interchange rate across debit, credit, and rewards cards comes out to roughly 1.5% (a realistic blended average for a mixed retail portfolio). Your cost is 400 × $50 × 1.7% (1.5% interchange + 0.2% markup) = $340, plus 400 × $0.08 = $32. Total monthly cost: $372.

In this example, interchange-plus saves this merchant about $188 a month, or roughly $2,250 a year — without changing anything about how the business accepts payments. The savings scale with volume: the higher your monthly processing amount, the more that markup gap compounds.

When flat-rate pricing makes more sense

Interchange-plus isn't automatically the better choice for everyone. Flat-rate pricing tends to make more sense in a few specific situations:

• You're just starting out. If your monthly volume is small — say, under $5,000–$10,000 a month — the markup difference on interchange-plus may not outweigh the value of simplicity and predictable statements.
• You want to budget without surprises. Flat-rate pricing means your percentage never changes based on which card a customer uses, which makes forecasting and bookkeeping simpler for very small operations.
• Your average ticket size is small and volume is unpredictable. Seasonal or highly variable businesses sometimes prefer the flat, easy-to-explain rate over a statement that requires more scrutiny each month.

When interchange-plus pricing makes more sense

• You process more than roughly $10,000–$15,000 a month. At this volume, the markup savings typically outweigh any added complexity.
• You want full transparency into your costs. Interchange-plus statements show you exactly what portion goes to the card networks and what portion goes to your processor, which is useful for cost analysis and vendor negotiations.
• Your customer base skews toward debit and basic credit cards. Because interchange-plus reflects the true cost of each card type, a business with mostly lower-interchange cards benefits the most.
• You're comfortable reading a slightly more detailed statement. Interchange-plus statements have more line items than flat-rate statements, but they're not complicated once you know what to look for (our companion guide on reading your processing statement walks through this in detail).

Common myths about interchange-plus pricing

A few misconceptions come up often enough that they're worth addressing directly.

"Interchange-plus is always cheaper."

Not always — it depends on your transaction volume and average ticket size. For very small or infrequent processors, the fixed per-transaction fee can sometimes offset the markup savings. It's worth running the numbers for your specific business rather than assuming.

"Flat-rate processors are hiding fees."

Not necessarily. A reputable flat-rate processor, like Harbour's flat-rate plans, is upfront about the all-in rate — there's nothing hidden, it's simply a single blended number instead of a broken-out one.

"Switching pricing models is complicated."

With most processors, switching models doesn't require new hardware or a new merchant account — it's usually a matter of updating your pricing agreement. Harbour, for example, lets merchants move between flat-rate and interchange-plus pricing as their processing volume changes.

How to decide which pricing model is right for your business

Rather than guessing, pull your last three months of processing statements and calculate your actual blended rate — the total fees you paid divided by your total card volume. If that blended rate is meaningfully higher than what an interchange-plus quote would come out to (interchange typically averages 1.5%–2% depending on your card mix, plus the markup), you're likely a good candidate to switch.

A processor should be able to review your statements and tell you, in plain terms, which model would have cost less over the same period. That's a useful gut check before committing either way — and it's exactly the kind of statement review Harbour offers as part of a free quote.

Frequently asked questions

Does Harbour Payments offer both pricing models?

Yes. Harbour offers both flat-rate and interchange-plus pricing, and merchants can switch between them as their processing volume grows. See our pricing page for current rates.

Is interchange-plus pricing harder to understand on a statement?

It has more line items than a flat-rate statement, but each one is straightforward once explained — interchange fee, network assessment, and processor markup. Most merchants find it easier to trust once they understand the breakdown.

Will my rate change if I switch pricing models?

Your effective rate may change, since it now reflects your actual card mix rather than a flat average — for most merchants processing meaningful volume, that means a lower blended rate overall.