Flat rate or interchange plus: which pricing model is costing you more?

Almost every merchant account is priced one of two ways. Which one you are on explains most of what you see on your statement, and switching between them is often a bigger lever than switching providers. Very few owners are ever told which they signed up for.

Flat rate, in plain terms

You pay one advertised percentage on every sale, sometimes with a small fixed amount per transaction. It does not matter whether the customer used a basic debit card or a premium travel rewards card. The price you pay is the same.

That is genuinely appealing. You can predict your costs, the statement is readable, and there is usually no monthly minimum or account fee buried underneath. For a business just starting out, or one processing modest volume, this is often the right answer and there is no shame in staying on it.

Interchange plus, in plain terms

The card brand cost is passed through to you exactly as it is charged, and your provider adds a stated markup on top. Your statement shows both parts separately, which is the important difference. You can see what the provider is keeping.

The trade is that your statement becomes harder to read and your costs vary month to month with your card mix. What you gain is transparency and, at volume, usually a lower total.

Why flat rate gets expensive as you grow

Under flat rate pricing, the provider is absorbing the difference between what the card brands charge them and what they charge you. On a cheap debit transaction that margin is wide. On an expensive rewards card it is thin. They are averaging across everybody.

The consequence is that a business whose customers mostly pay with basic debit cards is quietly subsidizing businesses whose customers pay with premium credit cards. And as your volume grows, that same percentage applies to a much larger number, with no mechanism for it to come down.

Interchange plus pricing, by contrast, gives you the actual cost of each transaction plus a markup you can negotiate. The cheap transactions stay cheap.

How to tell which you are on

Look at your statement. If you see one percentage applied to your whole volume, you are on flat rate. If you see a long breakdown of transaction categories with different percentages, and a separate line for your provider's markup, you are on interchange plus.

There is a third possibility that is worth knowing about. Tiered pricing sorts your transactions into buckets with names like qualified, mid-qualified, and non-qualified. It looks like interchange plus but the provider decides which bucket each transaction falls into, and that decision is not visible to you. If your statement uses those words, that is worth asking about.

Working out which is cheaper for you

You cannot answer this from the advertised rates. You need your effective rate, which is your total fees for a month divided by your total card volume for that month. Do it for three consecutive months so a slow month or a one-off annual fee does not distort it.

Then compare that figure against an interchange plus quote, adding in every monthly line item the new provider would charge: account fee, gateway, monthly minimum, PCI. A lower headline markup with three new monthly fees underneath can easily land higher than what you pay now.

So which should you choose?

Flat rate suits low volume, simple checkout, and owners who value a readable statement over the last fraction of a percent. Interchange plus suits a business with real volume, particularly one whose customers use a lot of debit cards, and owners who want to see what they are being charged for.

The honest summary is that flat rate is a convenience product. You pay a premium for simplicity. That is a perfectly reasonable thing to buy, right up until the premium gets larger than the convenience is worth. Only your own numbers can tell you where that line is.

Related reading

• How to audit your own statement for junk charges
• An honest look at Square
• Payment processing for contractors: Level 2 and Level 3 data

---

Luis Your Money Man is an Independent Sales Organization. This page carries no affiliate links. Product features and pricing change often, so treat this as a starting point and confirm current details with the provider before you decide. Last reviewed September 2026.