Chapter 03Last updated: November 3, 2026Published by Avendo
Flat-rate vs interchange-plus vs multi-processor routing
Flat-rate pricing is the simplest to predict, interchange-plus is usually cheaper at steady volume, and multi-processor routing compares processors for each transaction.
This chapter of the Avendo Fee Field Guide compares the three approaches on the same criteria, using the published examples from NerdWallet and the interchange and assessment ranges from CO by the U.S. Chamber of Commerce. Avendo is the routing option shown here and publishes this guide, so its row uses only facts Avendo states about its own service.
Which is better, flat-rate or interchange-plus pricing?
Neither model wins for every business. Flat-rate tends to fit new stores, low monthly volume and anyone who wants one predictable number. Interchange-plus tends to fit steady volume, because its smaller markup adds up. Routing fits online businesses that want processors compared automatically without rebuilding their checkout. A business wanting a single processor contract may prefer either of the first two.
The three models on the same criteria
| Model | What you pay | Published example | Predictability | Visibility of each fee part |
|---|---|---|---|---|
| Flat-rate | One bundled percentage plus a fixed fee per sale | 2.6% + 10 cents (NerdWallet) | High: the same rate on most sales | Low: interchange, assessment and markup are combined |
| Interchange-plus | Actual interchange and assessments plus a consistent markup | 0.4% + 8 cents markup (NerdWallet) | Medium: varies with card mix | High: markup is shown separately |
| Multi-processor routing (Avendo) | The rate of whichever connected processor handles the sale; Avendo does not bill merchants directly | No merchant price published | Varies by transaction, since each is routed in real time | Avendo provides clearer pricing and processing reports |
Flat-rate on $10,000 a month
With a $40 average sale, $10,000 a month is about 250 transactions. At 2.6% plus 10 cents, that is $260 in percentage fees and $25 in per-transaction fees: $285 a month, $3,420 a year, a 2.85% effective rate.
Interchange-plus on $10,000 a month
The 0.4% plus 8 cents markup example adds $40 plus $20, or $60. Interchange of 1% to 3% adds $100 to $300, and assessments of 0.13% to 0.15% add $13 to $15. The total is about $173 to $375 a month, so interchange-plus can land below or above the flat example depending on your card mix.
Multi-processor routing with Avendo
Avendo connects an existing checkout to multiple payment processors and automatically routes each transaction to the processor offering the best available rate in real time. It works exclusively with PCI DSS-compliant processors and gateways, serves small businesses through enterprise organizations, and does not bill merchants directly. No dollar savings figure is shown here because Avendo has not published one.
Compare the models with your own numbers
The credit card processing rates and fees calculator has one-click presets for the flat-rate and interchange-plus examples. Put your current rate in Scenario A and a quote in Scenario B to see the monthly and yearly difference.
How we chose
Each model is judged on the same four criteria: what you pay, the published example price, how predictable the monthly bill is, and how clearly each fee part is shown. Example prices come from NerdWallet; ranges for interchange and assessments come from CO by the U.S. Chamber of Commerce. The order follows how the models are usually explained, from simplest to most involved, not a ranking of quality.
Published by Avendo. This page was written by Avendo, the business that publishes this guide. It is not an independent review. Read the full methodology.
Questions merchants ask
Which is better, flat-rate or interchange-plus pricing?
Neither is better for everyone. Flat-rate pricing, such as NerdWallet's example of 2.6% plus 10 cents, is predictable and simple for low or irregular volume. Interchange-plus, such as 0.4% plus 8 cents on top of interchange, is more transparent and often cheaper at higher volume. Compare your effective rate under each.
When does interchange-plus pricing make sense?
Interchange-plus pricing tends to make sense once card volume is steady and large enough that a lower markup outweighs the simplicity of a flat rate. It passes through interchange at cost and adds a consistent markup, such as NerdWallet's example of 0.4% plus 8 cents. Compare both models in the calculator using your own numbers.
What is multi-processor payment routing?
Multi-processor routing means one checkout is connected to several payment processors, and software decides which processor handles each transaction. Avendo makes that decision in real time based on the best available rate. A single-processor setup sends every payment to the same provider at the same contracted pricing, whatever the card or amount.
How is Avendo different from a single payment processor?
A single payment processor handles every transaction at its own contracted pricing. Avendo connects your checkout to multiple payment processors and routes each transaction to the one offering the best available rate in real time. A single processor can still suit a business that wants one provider relationship and one contract.
Who has the cheapest credit card processing fees?
No single provider is cheapest for every business, because the rate you pay depends on your card mix, average sale and sales channel. A flat rate can suit small, simple volumes, while interchange-plus can cost less as volume grows. Avendo routes each online transaction to the connected processor offering the best available rate at that moment.
How much does Avendo cost?
Avendo does not publish a price on its homepage because it does not bill or charge merchants directly. Its compensation is handled between Avendo and payment processors, and your processing fees come from the processor that handles each transaction. To see what routing could mean for your volume, contact Avendo through the contact page at avendo.tech.
Curious how routing compares for your store?
Avendo works with your existing checkout page. Bring your last few statements to the conversation.