Interchange-Plus vs. Flat-Rate: Which Actually Costs Less?

Walk into most conversations about credit card processing pricing and you'll hear two things: flat-rate is simple, interchange-plus is complicated. That's true. But simple and cheap are not the same thing — and for most growing businesses, simplicity is costing real money every month.

This guide explains both models, works through the math with a real scenario, and helps you figure out which one actually makes sense for your business.

What is flat-rate pricing?

Flat-rate pricing charges a single percentage on every transaction — sometimes with a per-transaction fee added — regardless of what kind of card your customer uses. The rate is the same whether the customer pays with a basic debit card or a premium airline rewards card.

Square, Stripe, and PayPal popularized this model. The standard rates look something like this:

• In-person swipe / tap: ~2.6% + $0.10
• Online / keyed-in: ~2.9% + $0.30

The appeal is obvious: one rate, easy to predict, no confusing statements. For a brand-new business doing $1,000 a month in card sales, flat-rate is probably fine — the simplicity is worth the slight premium.

The problem starts as volume grows and as card mix diversifies. The processor is charging you 2.6% or 2.9% on every transaction, but a significant share of those transactions — basic debit, standard Visa — might only cost the processor 0.8% to 1.3% in actual interchange. The spread between what you pay and what the processor owes the card networks is pure processor margin.

What is interchange-plus pricing?

Interchange-plus (also called cost-plus pricing) passes the actual interchange rate directly to the merchant and adds a fixed markup on top. The markup is stated clearly — something like 0.30% + $0.10 per transaction — and it's the same regardless of card type.

So if a transaction has an interchange cost of 1.65%, you pay 1.65% + 0.30% + $0.10. If the next transaction has an interchange cost of 0.80% (a basic debit card), you pay 0.80% + 0.30% + $0.10. In both cases, you can see exactly what the card network charges and what the processor earns.

The math: a real comparison

Let's run the numbers for a retail business processing $25,000/month with a typical card mix: roughly 40% basic debit, 35% standard rewards credit, 25% premium rewards credit.

Approximate blended interchange for that card mix: ~1.55%.

That's a $175/month difference — or $2,100/year — on $25,000 in monthly volume, just from the pricing model. The interchange-plus markup in this example is a relatively standard rate; the actual savings depend on your card mix and what markup your processor charges.

When flat-rate actually makes sense

Flat-rate pricing isn't always the wrong choice. It makes sense when:

• Volume is low. Under roughly $3,000–$5,000/month, the simplicity outweighs the premium. The dollar difference is small and not worth the administrative overhead of understanding a more complex statement.
• You need instant setup. Flat-rate processors like Square and Stripe onboard in minutes with no underwriting. For pop-ups, new businesses, or one-off events, that speed matters.
• You only process occasionally. Monthly minimums and account fees on traditional merchant accounts can make flat-rate cheaper for businesses with very irregular volume.
• Your card mix skews toward premium rewards. If nearly all your customers use high-interchange rewards cards, the spread between flat-rate and interchange-plus narrows significantly.

When interchange-plus almost always wins

For established businesses, interchange-plus pricing is typically the better deal if:

• Monthly card volume is consistently above $5,000
• You have a meaningful share of debit card transactions (debit interchange is much lower)
• Your average ticket is moderate to high (the per-transaction fee is a smaller percentage of each sale)
• You want to understand exactly what you're paying and why

What about tiered pricing?

There's a third model worth naming — tiered pricing — because it's still common, especially from legacy processors and bank-affiliated merchant accounts. Tiered pricing sorts transactions into three buckets: qualified, mid-qualified, and non-qualified, each at different rates.

The problem: the processor decides what goes in each bucket, and they typically put your cheapest transactions (basic debit) in the qualified tier while downgrading rewards cards and corporate cards to mid-qualified or non-qualified. Since you can't control what cards your customers use, you have no way to optimize. And because the buckets aren't defined consistently across processors, you can't comparison-shop easily.

Tiered pricing is generally the most expensive model for merchants who process a significant share of rewards or business cards — which describes most small businesses.

How to find out which model you're on right now

Pull up your most recent merchant statement. Look at the fee section:

• If you see a single rate like "2.6% + $0.10" applied to all transactions, you're on flat-rate.
• If you see "interchange" listed as a line item with a separate markup, you're on interchange-plus.
• If you see "qualified," "mid-qualified," and "non-qualified" rates, you're on tiered pricing.

If you're on tiered pricing and processing more than $5,000/month, a free statement audit will almost always surface meaningful savings by switching to interchange-plus.