Interchange-plus vs flat-rate processing: compare the full monthly cost

Interchange-plus pricing separates underlying card costs from the provider's charge. Flat-rate pricing quotes a processing rate for a defined category of transactions. Neither label identifies the cheapest offer for every business. Compare the complete fee schedule against the same volume, payment count, card mix, channels, and countries.

Adyen describes Interchange++ as a model that tracks interchange and scheme fees at transaction level. Square publishes processing categories that vary by payment type and plan, with separate international transaction information. These examples show why a flat rate is not necessarily one universal percentage and why a small processor markup is not the whole interchange-plus cost.

For an interchange-plus proposal, obtain the definition of passed-through costs and the provider's percentage, per-transaction, and fixed charges. Ask how scheme fees, assessments, authorizations, cross-border activity, refunds, and other events appear. Different proposals can use similar names while placing charges in different lines of the schedule.

For a flat-rate proposal, identify which category applies to in-person, online, manually entered, stored-card, and invoice payments. Then check separate charges and subscription requirements. Do not apply an in-person headline rate to an ecommerce business simply because it is the first figure on the pricing page.

Request a sample statement with explanations for each line. Finance should be able to reproduce the charge from the agreed schedule. A quote that cannot be tied to transaction records will be difficult to review after volume or card mix changes.

The following example is entirely hypothetical and is not a quote from Adyen, Square, or another provider. Assume $100,000 of processed card volume across 500 payments. For the interchange-plus option, assume $1,750 of interchange, $150 of scheme costs, a provider charge of 0.30% plus $0.10 per payment, and a $50 monthly fee.

For the flat-rate option, assume 2.50% plus $0.10 per payment and no additional fees for this simplified population. The arithmetic compares only the stated assumptions. Actual proposals require all applicable categories and charges.

The interchange-plus option is $250 lower in that example. If its underlying card costs rise by more than $250 while the assumed flat-rate total stays unchanged, that result reverses. The comparison therefore depends on the payment population, not just the provider markup.

Run the calculation on several representative periods and a plausible future mix. Separate domestic and international cards, relevant card categories, online and in-person activity, and typical ticket sizes using the information available in your statements. Keep unknown components visible instead of filling them with a favorable guess.

Payment count matters independently of volume. A business with many small purchases can incur more per-transaction charges than one with the same dollar volume spread across fewer purchases. If average order value is changing, include that change in the forecast. Also test the effect of refunds and failed attempts under each actual fee schedule.

Some proposals include services the business would otherwise buy separately, such as point-of-sale software, payment tools, or reporting. Others charge separately for capabilities the team requires. List those costs beside processing so the total commercial comparison covers the same usable arrangement.

Keep cash access and risk terms in their own review. Settlement timing, reserves, payout options, and support can affect operations without changing the quoted processing percentage. A lower modeled fee does not establish that the provider supports the business's transaction types or onboarding requirements.

Read the term, minimum commitment, price-change provisions, cancellation conditions, and responsibility for any equipment or separate service contracts. A one-month fee comparison should not conceal a longer obligation. Obtain the completed schedules that will govern the account before approving the offer.

After launch, compare the actual transaction population and charges with the accepted proposal. Explain differences caused by volume, payment type, international activity, or separately billed services. Keep the fee model current enough that finance can distinguish a normal mix change from an unexpected charge.

Choose interchange-plus when its itemized economics and administrative requirements fit the business. Choose a flat-rate arrangement when its applicable categories and total cost make sense for the expected payments. The decision should rest on a reproducible comparison and acceptable operating terms, with the assumptions available for the next review.