Interchange-plus (IC+) bills the wholesale cost of each card, interchange plus assessments, then adds a published markup. Flat-rate bills one blended percentage, sometimes plus a per-item fee, on every card. Neither is automatically cheaper. Debit-heavy, steady volume usually pays less on IC+ because cheap debit is not priced like rewards credit. Low, seasonal, or new volume often prefers flat-rate because one predictable number is worth more than a few basis points. Compare them with effective rate: total processing fees divided by card volume for the same month.
These are two of six common pricing models. This page is only the IC+ versus flat fork. Typical processing fees are often described as 1.5 percent to 3.5 percent of the transaction plus a per-item fee (U.S. Chamber of Commerce, 4 Jun 2026). Treat that as a typical range, not a quote and not a Relyon rate.
What each model actually bills
Interchange-plus passes two layers at cost and discloses the third. Interchange goes to the issuing bank. Assessments go to the networks. The "plus" is the only number your provider sets: a percentage, a per-item fee, or both, for example 0.20% + $0.10 (illustrative). Your effective rate moves when mix moves. The markup should not, unless you signed a new schedule.
Flat-rate hides those three layers behind one blended number, for example 2.50% + $0.10 (illustrative). A basic debit card and a premium rewards card pay the same. You always know what a sale will net. You also pay a rewards-card rate on cheap debit, and you cannot see how much of the blended number is wholesale versus markup.
- Wholesale (interchange + assessments) billed at cost
- Markup 0.20% + $0.10 = $240
- Debit-heavy mix: $1,280 fees, 1.60% effective
- Rewards-heavy mix: $2,240 fees, 2.80% effective
- One blended rate on every card
- 2.50% + $0.10 = $2,080
- Same 2.60% effective on either mix
- You overpay debit and underpay rewards relative to cost
The figure is illustrative. It is not a quote. Change ticket size, debit share, or the two advertised numbers and the ranking can flip.
Why debit mix tilts toward IC+
Debit is a different wholesale floor from credit. Under the Federal Reserve's Regulation II, debit interchange received by issuers with $10 billion or more in assets is capped at 21 cents plus 5 basis points of the transaction, plus up to 1 cent if the issuer meets the fraud-prevention standard. Issuers under $10 billion are exempt (Federal Reserve, Regulation II). Credit is not capped that way.
Walk one $80 debit sale from a large issuer. Interchange at the cap is $0.21 + $0.04 = $0.25, plus up to $0.01 for fraud prevention. That is the issuer's fee, not your whole bill. Under IC+ you still add assessments at cost and the published markup. Under a 2.50% + $0.10 flat (illustrative), the same $80 costs $2.10 before monthly extras: $2.00 plus $0.10. The gap is the blended rate charging debit as if it were credit.
That is why a card-present shop with a large debit share often looks cheaper on IC+. The model does not invent a discount. It stops averaging cheap cards into expensive ones.
The reverse is also true. A rewards-heavy or card-not-present book has a higher wholesale floor. IC+ will show that floor. A well-priced flat rate can land at or below that IC+ effective rate, especially once you add the extra statement pages and the time to read them.
A worked month, two mixes (illustrative)
Hold the shop constant: $80,000 in card volume, 800 settled transactions, $100 average ticket. IC+ markup is 0.20% + $0.10. Flat-rate is 2.50% + $0.10. Monthly extras are left off both sides here so the model is the only moving part. On a real statement you add PCI, batch, statement, and gateway to both.
IC+ markup is the same in both mixes: 0.20% of $80,000 is $160, plus 800 × $0.10 is $80, for $240.
Mix A, debit-heavy (illustrative wholesale $1,040).
| Model | Wholesale | Markup / blended | Total fees | Effective rate |
|---|---|---|---|---|
| IC+ | $1,040 | $240 | $1,280 | 1.60% |
| Flat-rate | bundled | $2,080 | $2,080 | 2.60% |
Mix B, rewards-heavy (illustrative wholesale $2,000).
| Model | Wholesale | Markup / blended | Total fees | Effective rate |
|---|---|---|---|---|
| IC+ | $2,000 | $240 | $2,240 | 2.80% |
| Flat-rate | bundled | $2,080 | $2,080 | 2.60% |
Same quotes. Opposite winner. Mix A is the debit-heavy case the sales pitch forgets when it sells a single 2.50%. Mix B is the case a flat-rate quote can honestly win. If a rep shows you only Mix A or only Mix B, they are not comparing models. They are picking a slide.
Per-item fees hit both models. On this $100 ticket, $0.10 is 0.10% of the sale. On a $10 ticket it is 1.00%. A flat rate that also carries a high per-item fee is expensive twice on small tickets: once in the blend, once in the pennies.
When flat-rate is the honest trade
Flat-rate is not a trick. It is a product: predictability. You stop reconciling hundreds of interchange categories. You can forecast cost from volume. That is worth a premium when:
- Monthly volume is low or lumpy, so a 20-basis-point gap is smaller than the cost of reading the statement.
- The business is new, seasonal, or still finding its mix, and you do not yet have a stable debit/credit split to price.
- Staff cannot or will not audit an itemized statement, and a model you will not read cannot be the audit model.
The premium is real once volume is steady and debit is a large share. You are paying a blended rate on cards whose wholesale cost sits far below that blend. If you are in that spot and still on flat-rate, the question is not "is IC+ more honest." It is whether the extra basis points exceed the value of never opening the PDF.
Do not confuse flat-rate with tiered pricing. Tiered sorts volume into qualified, mid-qualified, and non-qualified buckets the provider defines. Flat-rate is one rate on every card. A teaser "qualified 1.79%" is not a flat rate. It is a bucket. Ask which one your statement actually is.
How to compare a real quote
Do not match a flat percentage to an IC+ markup. "2.50% versus 0.20% plus interchange" is not a comparison. One number includes wholesale. The other does not.
- Pull one full statement. Add every processing line. Divide by gross card volume. That is the effective rate you pay today.
- Write down mix: debit share, rewards share, keyed or e-commerce share, average ticket, transaction count.
- Price the IC+ quote on that month: estimated wholesale (or last month's interchange and assessments if the statement shows them) plus the published markup plus extras.
- Price the flat quote on the same month: blended rate times volume, plus per-item times count, plus extras.
- Stress mix. Repeat on a debit-heavy month and a rewards-heavy month if you have both. A flat rate that looks fine on December rewards will not look the same in a debit-heavy February.
If either quote will not run against last month's volume, you do not have a quote. You have a headline. If you want last month's PDF rebuilt as billed, run the analyzer and hold both quotes against the same sheet.
How to tell which one you are on
The sales deck is not evidence. The statement is.
You are on IC+ if you can find three blocks: interchange categories (often by brand and product), an assessments block, and one markup line such as "0.20% + $0.10." Count the markup lines. One disclosed plus is IC+. If interchange is missing and you still see a single percentage, that is not IC+, even if the proposal said "interchange."
You are on flat-rate if almost every card, debit and credit, posts at the same percentage, sometimes with a second rate for keyed, e-commerce, or American Express. There is no interchange detail to audit. The simplicity is the tell.
A statement can also be a blend that borrowed the IC+ name: a "plus" that is not pass-through, or a flat rate with a surcharge bolted on. If you cannot recompute last month's total from the published formula, the label is marketing.
Pick the model that matches ticket, mix, and whether you will actually read the statement. Then measure it every month the same way: total fees divided by card volume. The cheaper headline is not the cheaper bill until that division says so.
FAQ
Is interchange-plus cheaper than a flat rate? Not always. Interchange-plus usually costs less on steady, debit-heavy volume because cheap wholesale debit is billed at cost plus a published markup. Flat-rate can cost less, or close enough that simplicity wins, when volume is low or lumpy, or when rewards and card-not-present cards dominate the mix.
What is the difference between interchange-plus and flat-rate pricing? Interchange-plus itemizes interchange and assessments at cost, then adds a disclosed markup. Flat-rate charges one blended percentage, sometimes plus a per-item fee, on every card. The first moves with mix. The second does not.
When does flat-rate credit card processing make sense? When a single predictable number is worth more than a few basis points: new volume, seasonal months, or a book too small to justify reading a 12-page statement. Forecastability is the product. The blended rate is the price of that product.
Why is debit cheaper on interchange-plus? Debit interchange for issuers with $10 billion or more in assets is capped at 21 cents plus 5 basis points, plus up to 1 cent if fraud-prevention standards are met (Federal Reserve, Regulation II). Small issuers are exempt. Interchange-plus passes that floor through. A flat rate prices the same debit like every other card.
How do I compare an interchange-plus quote to a flat-rate quote? Hold one month of volume and mix constant. Price both quotes on that month, add every monthly extra, and divide total fees by card volume. That effective rate is the comparison. Do not match a flat percentage to an IC+ markup. They are different objects.
How can I tell which model I am already on? Read last month's statement, not the sales deck. Interchange-plus lists interchange categories, an assessments block, and one markup line. Flat-rate is one blended percentage on every card, sometimes with a second rate for keyed or American Express. If you cannot find those three IC+ blocks, you are not on IC+.
Sources
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