Flat-Rate vs Interchange-Plus: Which Pricing Costs You Less

Most processors quote one of two pricing models, and the choice can swing your effective rate by half a percentage point or more. Flat-rate is simple and predictable; interchange-plus is cheaper once you have volume. Here is how to tell which one is actually costing you more.

How the two models work

Flat-rate pricing charges one blended percentage on every sale regardless of card type, typically 2.6%-2.9% plus a fixed 10-30 cents per transaction. A $100 sale costs you the same whether the customer pays with a plain debit card or a premium rewards card, and there is usually no monthly fee. The processor absorbs the difference between cheap and expensive cards and keeps the spread.

Interchange-plus splits your cost into its two parts. You pay the interchange rate the card networks set (roughly 0.05%-2.3% depending on the card) plus a fixed markup the processor keeps, commonly 0.15%-0.50% plus 8-15 cents per transaction. The statement is longer and less predictable month to month, but you never overpay on a plain debit swipe, and the processor's cut is visible rather than buried in a blended rate.

Where interchange-plus starts to win

The trade-off comes down to volume. Flat-rate's convenience costs a premium of roughly 0.3%-0.6% over what interchange-plus charges on the same mix of cards. On low volume that premium is only a few dollars a month. On higher volume it compounds fast.

• Under $5,000/month: flat-rate usually wins, since interchange-plus plans often carry a $10-$30 monthly fee that erases the savings.
• $5,000-$10,000/month: it is close; interchange-plus pulls ahead if your average ticket is small or you take a lot of debit.
• $10,000-$25,000/month: interchange-plus usually wins, often saving 0.3%-0.5% of total volume even after monthly fees.
• Over $25,000/month: the gap is hard to ignore, and it is worth asking processors to quote their markup directly.

A worked example

Say you run $20,000 a month across 400 transactions, a $50 average ticket. On a flat-rate plan at 2.75% plus 15 cents, you pay about $550 in percentage fees plus $60 in per-transaction fees: roughly $610 a month, with no monthly fee.

On interchange-plus, assume your blended interchange lands near 1.8% and the processor adds 0.25% plus 10 cents. That is about $410 in percentage fees plus $40 in per-transaction fees, so $450, plus a $15 monthly fee: $465 total. You save about $145 a month, or roughly $1,700 a year, for the cost of reading a denser statement.

Which to choose

If you are new, seasonal, or running under $5,000 a month, flat-rate is the sensible default: predictable, no monthly fee, and easy to reconcile. The premium is small in absolute dollars, and your time is better spent elsewhere.

If you are consistently above $10,000 a month, get an interchange-plus quote and compare it against three months of your real statements. Ask for the markup in basis points and cents, and confirm no separate monthly minimum or statement fee is hiding the savings. The number that matters is your effective rate: total fees divided by total volume.