Under interchange-plus plans, merchant credit card processing fees are calculated via tables issued by credit card companies.
Credit card type and transaction method are the two factors used to determine these processing fees.
For instance, to process an in-person purchase made with a Visa preferred card, the current interchange-plus rate is 2.10 percent plus $0.10. To process a $100 sale at that rate, the merchant will have to pay an additional $2.20.
Although generally more affordable than tiered plans, interchange-plus plans are not without drawbacks. The most significant is that they're vulnerable to marketplace volatility.
If Visa suddenly decides to raise their preferred card rate to 3.10 + $0.15, merchants will find themselves on the hook for that price increase.