When you sign up for merchant services, one of the most important decisions you'll make — often without realizing it — is your pricing model. The two most common options are interchange-plus and flat-rate pricing, and the difference between them can easily amount to hundreds of dollars per month for a mid-size business.

Most merchants end up on flat-rate pricing because it's what the major consumer-facing processors default to. That's not always the wrong choice — but it's rarely the optimal one for businesses processing significant volume.

Here's what you need to know.

Before comparing pricing models, it helps to understand what interchange actually is.

Every time a customer pays with a credit or debit card, the card network (Visa, Mastercard, Discover, Amex) charges a fee to process that transaction. This fee — called the interchange rate — goes primarily to the card-issuing bank as compensation for the risk and cost of extending credit.

Interchange rates are set by the card networks and published publicly. They vary based on:

• Card type — rewards cards, business cards, and premium cards carry higher interchange than basic debit cards
• Transaction type — card-present (in-person) transactions are cheaper than card-not-present (online/phone) transactions
• Merchant category — some industries get preferential rates (utilities, government) while others pay more (travel, restaurants)
• Transaction amount — some categories have tiered rates based on ticket size

There are hundreds of interchange categories. A basic consumer Visa debit card swiped in person might cost 0.05% + $0.22. A premium Visa Infinite rewards card keyed in manually might cost 2.40% + $0.10. The spread is enormous.

With flat-rate pricing, you pay the same percentage on every transaction regardless of card type, transaction method, or amount. Square, Stripe, and PayPal all use this model.

Example: 2.6% + $0.10 on every in-person swipe.

• Predictable. You always know exactly what you'll pay.
• Simple. No statement analysis required.
• Easy to get started. No underwriting, no lengthy application.

Flat-rate processors charge you the same rate whether your customer pays with a basic debit card (interchange: ~0.05% + $0.22) or a premium rewards card (interchange: ~2.10% + $0.10). On that debit card transaction, the processor is pocketing the difference between 2.6% and 0.05% — a significant margin.

For businesses where most customers pay with basic debit cards or low-tier credit cards — grocery stores, gas stations, convenience stores — flat-rate pricing is particularly expensive.

Flat-rate pricing tends to favor: Very low-volume businesses, businesses that value simplicity over savings, and businesses just getting started that need quick setup without underwriting.

With interchange-plus pricing, you pay the actual interchange cost for each transaction plus a fixed markup charged by your processor.

Example: Interchange + 0.30% + $0.10 per transaction.

So if a customer pays with a basic Visa debit card (interchange: 0.05% + $0.22), you pay 0.35% + $0.32. If they pay with a premium rewards card (interchange: 2.10% + $0.10), you pay 2.40% + $0.20.

• Transparent. You can see exactly what the card networks charge and exactly what your processor charges on top.
• Usually cheaper. For most businesses processing over $10,000/month, interchange-plus is less expensive than flat-rate.
• Fair. You pay more when the underlying cost is higher (premium rewards cards) and less when it's lower (basic debit).

Your monthly statement will show many different line items — one for each interchange category that appeared in your transactions. This makes statements harder to read but gives you full visibility into your costs.

Interchange-plus pricing tends to favor: Established businesses processing $10,000+/month, businesses with a mix of card types, and any merchant who wants full transparency into their processing costs.

Let's run the numbers on a business processing $50,000/month with a typical card mix (60% debit/basic credit, 40% rewards/premium cards).

Flat-rate at 2.6% + $0.10 (avg ticket $75, ~667 transactions):

• Percentage fees: $50,000 × 2.6% = $1,300
• Per-transaction fees: 667 × $0.10 = $66.70
• Total: ~$1,367/month

Interchange-plus at interchange + 0.30% + $0.10:

• Blended interchange (estimated): ~1.5% = $750
• Processor markup: $50,000 × 0.30% = $150
• Per-transaction fees: 667 × $0.10 = $66.70
• Total: ~$967/month

Difference: ~$400/month, or $4,800/year.

That's a meaningful number — and this example uses conservative assumptions. Businesses with higher average tickets or a higher proportion of debit card transactions would see even larger savings.

There's a third model worth mentioning: tiered pricing (also called "bundled" pricing). This is where transactions are grouped into qualified, mid-qualified, and non-qualified tiers, each with a different rate.

Tiered pricing is generally the worst option for merchants. The processor controls which tier each transaction falls into, the criteria are rarely disclosed, and most transactions end up in the more expensive tiers. It's designed to look simple while obscuring the true cost.

If your current processor uses tiered pricing, a review is almost certainly worth your time.

Look at your monthly processing statement. If you see:

• A single rate applied to all transactions → flat-rate
• Line items showing "interchange" costs plus a separate markup → interchange-plus
• "Qualified," "mid-qualified," "non-qualified" categories → tiered

If you can't tell from your statement, call your processor and ask directly: "What pricing model am I on?"

For very small businesses or those just getting started, flat-rate pricing's simplicity can be worth the premium. For any business processing $10,000 or more per month, interchange-plus pricing almost always results in lower costs — often significantly lower.

The catch is that interchange-plus pricing requires working with a processor that offers it, which typically means going through a broker or ISO rather than signing up directly with a consumer-facing platform.

That's exactly what we do at Optix Merchant Group. We evaluate your current pricing, model out what interchange-plus would cost you based on your actual transaction history, and connect you with processors offering competitive terms — at no cost to you.

If you'd like to know what you're actually paying versus what you could be paying, send us your last two statements and we'll run the numbers.

Optix Merchant Group is an independent merchant services advisory firm based in Texas. We help businesses across the country find better payment processing arrangements.