Flat-rate payment processing is usually easier to predict, while interchange-plus pricing makes the processor's markup easier to see and can reduce costs when your underlying card mix is inexpensive. Neither model is automatically cheaper. The better choice depends on transaction size, card type, sales channel, monthly volume, fixed account fees, and the exact markup in your quote.
This guide focuses on U.S. merchants. Published processor rates and card-network schedules can change, so compare current quotes using your own transaction history rather than choosing a processor from a headline percentage alone.
| Pricing model | What you pay | Main advantage | Main limitation |
|---|---|---|---|
| Flat rate | A predetermined percentage plus, often, a fixed transaction fee | Simple forecasting and easy statements | The processor's margin is bundled into the rate |
| Interchange plus | Underlying interchange/network costs plus a stated processor markup | Greater cost transparency and potential savings on lower-cost transactions | Monthly cost moves with your card and transaction mix |
Contents
- How the two pricing models work
- How flat-rate processing works
- How interchange-plus works
- Worked $50,000 monthly example
- How to calculate your break-even point
- Fees the headline rate can hide
- Which pricing structure fits your business?
- Questions to ask before signing
Payment processor pricing has more layers than the headline rate
A merchant may see a processor advertise something as simple as 2.6% plus 15 cents or 2.9% plus 30 cents. Behind a card transaction, however, there can be several economic components.
One component is interchange. Mastercard explains that interchange rates are generally paid by acquiring institutions to card issuers and are only one component of the merchant discount rate charged for card acceptance. Visa similarly explains that merchants generally pay their financial institution a merchant discount covering payment-processing services rather than literally sending an interchange payment directly to Visa.
You can review the card networks' explanations on the Visa interchange and merchant fee page and Mastercard's U.S. interchange page.
The important point for a business owner is that the underlying cost is not necessarily identical for every transaction. Card product, debit versus credit, merchant category, transaction channel and qualification criteria can affect the applicable interchange treatment.
A processor then has to recover its own costs and earn a margin. The main pricing question is whether that margin is bundled into an all-in rate or shown more explicitly on top of pass-through costs.
How flat-rate payment processing works
With flat-rate pricing, the processor generally quotes one predetermined rate for a particular transaction channel. A business can therefore estimate fees without first identifying the exact interchange category of every card.
For example, as checked on September 26, 2026, Stripe's U.S. standard pricing lists 2.9% plus 30 cents for a successful domestic card transaction. Stripe also offers custom arrangements, including interchange-plus pricing, for qualifying businesses.
Square's U.S. pricing currently varies by plan and payment channel. Its Free plan lists 2.6% plus 15 cents for a tap, dip or swipe transaction and 3.3% plus 30 cents for an online payment. Square's paid plans publish different rates, and the company says businesses processing more than $250,000 per year can discuss eligibility for custom pricing.
These examples also show why “flat rate” does not necessarily mean one rate for absolutely everything. A processor may charge different flat rates for card-present, online, manually entered, international or other transaction categories.
Why businesses choose flat-rate pricing
- The arithmetic is easy to understand.
- Monthly processing expense can be easier to forecast.
- Small businesses may avoid complicated merchant statements.
- A processor may bundle POS software, checkout tools, invoicing or other services that have operational value.
- Some plans have no monthly processing-account subscription charge.
The trade-off is that you normally cannot look at the headline processing rate and determine exactly how much of each transaction represented interchange, network expense and processor margin.
How interchange-plus pricing works
Interchange-plus, sometimes written as interchange+, IC+ or cost-plus, takes a different approach. The processor passes through specified underlying card costs and adds its own stated markup.
A simplified structure might look like this:
Transaction cost = interchange/network pass-through costs + processor percentage markup + processor per-transaction markup
That does not mean every interchange-plus provider structures statements identically. You still need to determine which assessments, network charges, gateway fees, account fees and other items are included or passed through separately.
As a current real-world example, Helcim publishes interchange-plus pricing. For monthly card volume from $0 to $50,000, its published U.S. processor margin is currently interchange plus 0.40% and 8 cents for in-person transactions, and interchange plus 0.50% and 25 cents for keyed and online transactions. Its published margins fall at higher volume tiers.
Helcim's U.S. fee disclosure further explains that card-association fees, network fees and interchange are passed through while the processor adds a percentage and transaction-dollar margin.
This separation is the main attraction of interchange-plus: if a transaction has a relatively inexpensive underlying card cost, a merchant can potentially receive more of that advantage rather than paying the same bundled rate used for a more expensive card transaction.
The opposite is also possible. When the underlying card cost is high, the merchant bears that higher cost instead of being protected by one predictable bundled percentage.
Worked example: $50,000 a month in card sales
The following numbers are an illustrative scenario, not industry averages and not a quote from a processor. They are deliberately simplified to show how the two formulas behave.
Assume a business has:
- $50,000 in monthly card sales
- 1,000 transactions per month
- $50 average transaction size
- Mostly card-present sales
Option A: flat rate of 2.6% plus 15 cents
Percentage fee:
$50,000 × 2.6% = $1,300
Transaction fees:
1,000 × $0.15 = $150
Total:
$1,300 + $150 = $1,450 per month
Effective processing rate:
$1,450 ÷ $50,000 = 2.90%
Option B: interchange-plus
Now suppose the business is quoted a processor markup of 0.40% plus 8 cents per transaction. For this example only, assume its combined pass-through interchange and network expense happens to average 1.75% plus 10 cents per transaction during the month.
Again, 1.75% plus 10 cents is an invented assumption for the illustration, not an estimate of what your business should expect.
Pass-through percentage cost:
$50,000 × 1.75% = $875
Pass-through transaction cost:
1,000 × $0.10 = $100
Processor percentage markup:
$50,000 × 0.40% = $200
Processor transaction markup:
1,000 × $0.08 = $80
Total interchange-plus cost:
$875 + $100 + $200 + $80 = $1,255
Effective processing rate:
$1,255 ÷ $50,000 = 2.51%
In this particular scenario, interchange-plus costs $195 less for the month before considering any additional recurring, gateway, hardware or account fees.
Now change only the underlying card cost
This is where the comparison becomes useful rather than decorative arithmetic.
Suppose the same business has a more expensive card mix and its illustrative pass-through cost rises to 2.35% plus 10 cents per transaction.
The pass-through portion becomes:
($50,000 × 2.35%) + (1,000 × $0.10) = $1,275
Add the same $280 processor markup:
$1,275 + $280 = $1,555
In that hypothetical month, the interchange-plus arrangement would cost $105 more than the $1,450 flat-rate example.
That is why a blanket rule such as “interchange-plus is always cheaper once you process a certain dollar amount” is too crude. Volume matters, but so do card mix, transaction count, average ticket and every fixed fee in the contract.
How to calculate your own break-even point
The strongest comparison uses your own processing history rather than a processor's promotional savings estimate.
Collect at least three recent merchant statements and record four figures for each month:
- Total card sales volume.
- Total number of transactions.
- Total processing-related fees actually paid.
- Any monthly, gateway, PCI, equipment or account fees that would continue under the new provider.
Your current effective rate is:
Total processing fees ÷ total card sales × 100
For example, if you processed $40,000 and paid $1,120 in total processing charges:
$1,120 ÷ $40,000 = 2.80%
Do not stop there, because two businesses with a 2.80% effective rate can have very different transaction economics. One might process 200 large invoices while another processes 4,000 small retail purchases.
Build both quotes using the same transaction data
For a flat-rate quote:
Estimated flat-rate cost = monthly volume × quoted percentage + transaction count × quoted transaction fee + recurring fees
For an interchange-plus quote:
Estimated IC+ cost = actual or realistically estimated interchange/network costs + processor percentage markup + processor transaction markup + recurring fees
The tricky variable is the first part of the interchange-plus formula. Ask the prospective processor whether it can reprice a recent statement or provide a transaction-level comparison using your actual card mix.
If a salesperson simply substitutes a low assumed interchange percentage without examining your card profile, the comparison can become an optimism machine with a calculator attached.
Compare more than the percentage rate
A lower advertised processing rate can lose its advantage once additional charges enter the invoice. Compare the complete cost structure.
| Cost to check | Why it matters |
|---|---|
| Percentage markup | Grows directly with card volume. |
| Per-transaction fee | Can dominate costs when average tickets are small. |
| Monthly or statement fee | Can make a low-volume interchange-plus account less attractive. |
| Gateway fee | May be separate from acquiring or processing charges. |
| PCI-related fee | Some providers bundle compliance tools; others charge separately. |
| Equipment or POS subscription | Hardware and software can outweigh a small processing-rate difference. |
| Chargeback or dispute fee | Important for businesses with higher dispute frequency. |
| International-card surcharge | Relevant when customers frequently use foreign-issued cards. |
| Currency-conversion fee | Can be separate from the ordinary card-processing rate. |
| Instant-transfer fee | Matters if the business frequently pays to accelerate settlement. |
| Contract or termination charge | Can materially increase the cost of switching. |
Also compare what the processor includes. A business that genuinely uses inventory management, appointments, invoicing, recurring billing or ecommerce software should not value the payment component in isolation.
Flat rate vs interchange plus: which structure fits your business?
Think in terms of operating fit rather than trying to crown one pricing model the universal winner.
| Business situation | Pricing structure worth examining closely | Reason |
|---|---|---|
| New or low-volume business | Flat rate | Simple setup and low fixed overhead may matter more than optimizing every basis point. |
| Business that values predictable fee calculations | Flat rate | Bundled pricing is easier to budget before the month's card mix is known. |
| Established merchant with meaningful card volume | Compare both | Small percentage differences become significant, making a detailed quote worthwhile. |
| Merchant with substantial lower-cost debit or qualifying card-present activity | Interchange plus | Lower underlying costs can flow through instead of being absorbed inside a bundled rate. |
| Business accepting many expensive card categories or card-not-present transactions | Compare both carefully | Higher pass-through costs can reduce the advantage of interchange-plus pricing. |
| Business with thousands of tiny purchases | Compare per-transaction charges first | A few cents per transaction can matter as much as the percentage rate. |
| High-volume merchant eligible for custom pricing | Request multiple custom quotes | Published standard rates may no longer be the relevant benchmark. |
Remember that processor pricing is negotiable in some situations. The relevant comparison may not be “standard flat rate versus standard interchange-plus.” It could be discounted flat pricing from one processor against interchange-plus from another.
Stripe, for example, currently lists IC+ and discounted flat rates among the structures available through custom pricing. Square also tells merchants processing more than $250,000 annually to ask about custom processing pricing.
Questions to ask a payment processor before signing
- What is your processor markup? If the quote is interchange-plus, ask for the percentage markup and per-transaction markup separately.
- Which card-network costs are passed through? Ask how interchange, assessments and other network charges appear on the statement.
- What recurring charges apply? Include monthly, annual, gateway, statement, PCI, platform and minimum-processing fees.
- How do card-present and card-not-present transactions differ? Online, manually keyed and card-on-file transactions may have different economics.
- What happens with international cards, currency conversion, refunds and disputes? These can materially change the real cost for some businesses.
- Is there a contract or early-termination obligation? A small processing discount may not compensate for an expensive long-term commitment.
- Can you reprice my recent statements? Ask the provider to apply its proposed pricing to your actual recent volume, transaction count and card mix.
Do not compare processors using percentage rates alone
An offer of 2.4% is not automatically cheaper than an offer of 2.6%. The first could include a larger transaction charge, software subscription, gateway fee or monthly minimum. Likewise, interchange plus 0.30% does not mean your total processing cost is 0.30%. The underlying interchange and network costs still have to be paid.
A useful quote should therefore let you estimate the total dollars leaving the business, not merely highlight the smallest percentage on the proposal.
Average ticket size deserves particular attention. On a $10 sale, a 30-cent transaction fee alone represents 3% of the purchase before any percentage fee is added. On a $500 sale, the same 30 cents is almost negligible.
This is why restaurants, professional services firms, ecommerce stores and small-ticket retailers can reach different conclusions even when their monthly sales volume is identical.
Bottom line
Flat-rate pricing buys simplicity and predictability. Interchange-plus separates more of the underlying payment cost from the processor's stated margin. Either can produce the lower total bill.
Your next step is simple: export three recent processing statements, calculate your current all-in effective rate, record your monthly transaction count and average ticket, and ask competing processors to price the same activity. Include recurring software, gateway, hardware, dispute and account charges before comparing totals.
If the difference between two quotes is only a few hundredths of a percentage point, also consider integration quality, reliability, settlement timing, support and the cost of changing systems. A payment processor is plumbing for your revenue stream; the cheapest pipe is not useful if it leaks operational headaches into the business.
Sources and current rate references
- Visa: U.S. processing fees, interchange and merchant rules
- Mastercard: U.S. merchant interchange rates and explanation
- Stripe: U.S. pricing
- Square: U.S. plans and payment-processing pricing
- Helcim: interchange-plus pricing and volume tiers
This article is for general educational purposes. Processing rates, network fees, eligibility and contractual terms can change, and your actual cost depends on your transactions and provider agreement.
