Educational Guide
The pricing model you choose for payment processing has a direct impact on your total cost — often more than the specific rate you negotiate. Understanding flat-rate, interchange-plus, and membership pricing helps you make a more informed comparison between processors.
Last updated: June 17, 2026
Quick Answer
Flat-rate pricing charges a fixed percentage on every transaction, making costs predictable. Interchange-plus pricing charges the actual interchange rate plus a fixed processor markup — typically lower at moderate to high volumes. For businesses processing under $10,000/month, flat-rate is simpler. Above that, interchange-plus usually saves money.
Flat-rate pricing charges a single fixed percentage and per-transaction fee on every card transaction, regardless of card type. For example, a processor might charge 2.6% + $0.10 per in-person transaction and 2.9% + $0.30 per online transaction.
The main advantage of flat-rate pricing is simplicity and predictability: you always know what you'll pay per transaction. This makes it easy to estimate monthly processing costs and build pricing into your products.
The main disadvantage is that flat-rate pricing averages across all card types. When a customer uses a basic debit card (which carries a low interchange rate), you pay the same rate as when they use a premium rewards credit card (which carries a higher interchange rate). For businesses with a favorable card mix — many debit and basic credit card transactions — flat-rate pricing can cost more than interchange-plus.
Interchange-plus pricing charges merchants the actual interchange rate for each specific card transaction, plus a fixed processor markup (the 'plus'). For example, a processor might charge interchange + 0.30% + $0.10 per transaction.
This structure is more transparent because you can see exactly how much goes to the card network (interchange) and how much goes to the processor. The markup is the negotiable component; interchange and assessment fees are set by card networks and are not negotiable.
At moderate to high processing volumes, interchange-plus typically produces a lower effective rate than flat-rate pricing — because many transactions (especially in-person debit and basic credit) have interchange rates well below the flat-rate floor. However, the monthly statement is more complex to read, and your costs fluctuate based on card mix.
Membership pricing (sometimes called subscription pricing) is a third model where merchants pay a fixed monthly fee in exchange for wholesale or near-wholesale interchange pass-through rates, often with a small flat per-transaction fee. Stax Pay is a current example of this approach.
The monthly membership fee replaces the processor's percentage markup. Because you're paying interchange at near-cost with no percentage markup, the effective rate at high volumes can be significantly lower than either flat-rate or standard interchange-plus.
There is no universal monthly-volume threshold where membership pricing becomes more cost-effective. Compare your card mix, transaction count, current fee structure, and the available plan terms before deciding.
Start by knowing your current or estimated processing volume and average transaction size. Then calculate your effective rate under each model.
For flat-rate: multiply your transaction count by the flat rate + per-transaction fee. For interchange-plus: estimate your blended interchange rate (typically 1.5%–2.0% for a mixed in-person consumer card mix) and add the processor markup. For membership: add the monthly fee to the estimated transaction fees (per-transaction fee × transaction count).
The model with the lowest total monthly cost is the right fit for your volume. Use the Cost Calculator on ProcessorFit to estimate based on your specific inputs.
Note: Your effective rate — total processing fees divided by total processing volume — is the most accurate way to compare processors across different pricing models.
Avoid these common errors when evaluating processor pricing:
Use this decision guide to identify the right pricing model for your business:
Not always. At lower processing volumes (under $5,000–$10,000/month), the simplicity of flat-rate may outweigh any savings from interchange-plus. At moderate to higher volumes, interchange-plus typically produces a lower effective rate. Calculate your specific cost under each model using your actual volume and card mix.
Your effective rate is total processing fees divided by total processing volume, expressed as a percentage. For example, if you paid $250 in fees on $10,000 in volume, your effective rate is 2.5%. Effective rate is the most useful number for comparing processors across different pricing models.
The interchange and assessment fee components are set by card networks and are non-negotiable. The processor markup — the 'plus' in interchange-plus — is negotiable, especially at higher processing volumes. Monthly fees and per-transaction fees are also sometimes negotiable.
The break-even point depends on your monthly membership fee, your card mix, and the alternative pricing model you're comparing against. A rough rule of thumb is $50,000/month, but your specific break-even may be higher or lower. Use the Cost Calculator to estimate based on your inputs.
Use Fit Check to identify providers that may deserve closer research based on your business profile, or open the Cost Calculator to estimate your fees.