The short answer
- Pick a flat rate if you’re new, small or seasonal, or you just want a bill you can predict. PayPal POS charges 2.29% + 9¢ in person and Square Free charges 2.6% + 15¢, both with no monthly fee.
- Look at interchange-plus once your card sales are steady and growing. Helcim publishes a markup that shrinks with volume. Stax swaps the percentage markup for a monthly subscription.
- Either way, compare totals, not headlines. A flat rate is the whole price. An interchange-plus markup is only part of it.
How each model works
Every card payment has two costs inside it. One is interchange, which goes to the bank that issued your customer’s card. The other is what your provider keeps.
Visa says it uses interchange “as transfer fees between acquiring banks and issuing banks,” and that merchants instead “negotiate and pay a ‘merchant discount’ to their financial institution” (Visa). In plain words, interchange is built into what your provider charges you. The pricing model decides whether you can see it.
Interchange isn’t one number. For debit cards, the Federal Reserve caps interchange for banks with $10 billion or more in assets at “$0.21 plus 0.05 percent multiplied by the value of the transaction, plus a $0.01 fraud-prevention adjustment, if eligible.” Smaller banks are exempt. In 2024, covered debit payments averaged 23¢ in interchange (0.47% of the sale), while exempt debit payments averaged 51¢ (1.21%) (Federal Reserve). That rule covers debit cards only.
Flat rate
The provider rolls everything into one rate. You pay the same on a cheap debit card and a premium rewards card. Published in-person flat rates:
- PayPal POS: 2.29% + 9¢
- Square: 2.6% + 15¢ on Square Free (2.5% + 15¢ on Plus, 2.4% + 15¢ on Premium)
- Shopify (Basic plan): 2.6% + 10¢
- Chase: 2.6% + 10¢
- Stripe: 2.7% + 5¢
The upside is simplicity. The downside is that the rate has to be high enough to cover the expensive cards, so on cheaper cards you pay more than the real cost.
Interchange-plus
You pay the actual interchange on each card, plus a markup. Published markups:
- Helcim: interchange + 0.40% + 8¢ in person, and interchange + 0.50% + 25¢ keyed or online, for up to $50,000 a month. The in-person markup drops with volume, down to 0.15% + 6¢ at $1 million to $5 million a month.
- Stax: “0% markup on interchange,” plus 8¢ per in-person sale and 15¢ per keyed or online sale. You also pay a subscription: $99 a month for up to $150,000 a year in processing, $139 for $150,000 to $250,000, and “$199+” above that.
- Stripe lists a custom package with “IC+ pricing” for “businesses with large payments volume or unique business models.” It doesn’t publish those rates.
Remember, these are markups only. Your real cost is interchange plus the markup. Helcim says that “for most merchants,” its total in-person effective rate is “near or below 2%” (Helcim’s claim, not ours). Stax doesn’t publish a total.
Side by side
- PayPal POSVisit PayPal POS
Flat rate
- In person
- 2.29% + 9¢
- Online
- 2.99% + 49¢
- Monthly
- $0 · Free POS app
- Contract
- No contract stated
- SquareVisit Square
Flat rate
- In person
- 2.6% + 15¢
- Online
- 3.3% + 30¢
- Monthly
- $0 · Free plan
- Contract
- No contract
- StripeVisit Stripe
Flat rate
- In person
- 2.7% + 5¢
- Online
- 2.9% + 30¢
- Monthly
- $0 · Reader bought separately
- Contract
- No contract
- HelcimVisit Helcim
Interchange-plus
- In person
- Interchange + 0.4% + 8¢
- Online
- Interchange + 0.5% + 25¢
- Monthly
- $0 · No monthly fee
- Contract
- No contract, no cancellation fee
- StaxVisit Stax
Membership
- In person
- Interchange + 8¢
- Online
- Interchange + 15¢
- Monthly
- Not published
- Contract
- Not published
Prices checked Oct 19, 2026 on each provider's own pricing page (how we check). "Interchange +" means the provider publishes only its markup. You also pay the card networks' interchange fee on top.
One sale, two ways to pay for it
Here’s a $50 in-person sale on a debit card from a large bank, the kind covered by the Federal Reserve cap. These are our estimates from published rates.
Flat rate:
| Provider | Published rate | Fee on $50 |
|---|---|---|
| PayPal POS | 2.29% + 9¢ | about $1.24 |
| Stripe | 2.7% + 5¢ | $1.40 |
| Square Free | 2.6% + 15¢ | $1.45 |
Interchange-plus: the most interchange a covered bank can charge on $50 is 21¢ + 0.05% of $50 (about 3¢) + 1¢ if eligible, so about 25¢.
| Provider | Markup on $50 | Plus interchange (max) | Total |
|---|---|---|---|
| Helcim | 0.40% + 8¢ = 28¢ | about 25¢ | about 53¢ |
| Stax | 8¢ | about 25¢ | about 33¢, plus the monthly subscription |
So on this debit card, interchange-plus costs well under half the flat rate. Helcim makes a similar point: it says US PIN debit through its interchange-plus pricing can often come in “below 1%” (Helcim’s claim).
Now the other side. A debit card from a smaller bank isn’t capped, and the Fed’s 2024 average for those was 51¢. Credit cards aren’t covered by the debit rule. Your provider may also pass on other card network fees. On interchange-plus, every one of those lands on your bill. On a flat rate, the provider absorbs them. That’s the trade.
When a subscription beats a percentage markup
Stax and Helcim both charge 8¢ per in-person sale. The difference is Stax’s subscription against Helcim’s 0.40%. By our estimate, at a few monthly volumes:
| Monthly card sales | Helcim’s 0.40% | Stax subscription |
|---|---|---|
| $12,500 ($150,000 a year) | $50 | $99 |
| $20,000 ($240,000 a year) | $80 | $139 |
| $50,000 ($600,000 a year) | $200 | $199 and up |
Below roughly $50,000 a month, Helcim’s percentage costs less than Stax’s subscription. Around $50,000 they’re close, and Stax’s top tier is listed only as “$199+,” so get the exact number in writing. Above $50,000 a month, Helcim’s markup also drops, to 0.35% + 7¢. Stax says “the more you process, the more you save” (its claim), and its page says “No cancellation fees (long term contracts),” which is unclear. Ask Stax to confirm the term.
Who each model suits
A flat rate suits you if:
- You’re new, small or seasonal, and a month can be slow.
- You want to check your bill in 10 seconds.
- Many of your sales are small, and you’d rather not read dozens of card categories.
Skip it if your volume is steady and much of it is debit. You’re likely paying a lot for that simplicity.
Interchange-plus suits you if:
- You have steady card sales, roughly in the tens of thousands a month or more.
- Many customers pay by debit, or you sell in person with lower-cost cards.
- You want to see what the card networks charge, and what your provider keeps.
Skip it if you can’t tell whether a bill went up because of your card mix or your provider.
How to decide
- Find your effective rate: total fees divided by total card sales, from last month’s statement.
- Put your numbers into the fee calculator to see what the same month costs at published flat rates.
- Ask an interchange-plus provider for a written quote based on that same statement. Compare the totals, not the markups.
Keep reading
- Credit card processing fees, explained: every line on a US statement.
- Compare payment processors: every provider side by side.
- Full breakdowns: Helcim, Stax, Square, Stripe, PayPal POS.
Common questions
What is interchange-plus pricing?
It's a way of pricing card payments in two parts. You pay the interchange fee, which goes to the bank that issued your customer's card, plus a markup your provider keeps. Helcim, for example, publishes a markup of 0.40% + 8¢ per in-person sale for businesses processing up to $50,000 a month. The interchange part changes with each card.
Is interchange-plus cheaper than a flat rate?
Often, once you have steady volume, but not always. A flat rate has to cover the most expensive cards, so you overpay on cheaper ones, like many debit cards. With interchange-plus you pay the real card cost, which you can't know in advance. The fair test is your own statement: total fees divided by card sales, compared to a quote.
Who should stick with a flat rate?
New businesses, seasonal businesses and anyone with low or uneven sales. Square Free and PayPal POS have no monthly fee, so a slow month costs nothing extra. Flat rates are also easy to check. At PayPal POS's 2.29% + 9¢, a $100 card sale costs $2.38, whatever card your customer uses.
Is Stax really 0% markup?
Stax publishes "0% markup on interchange," but that isn't free. It charges 8¢ per in-person sale and 15¢ per keyed or online sale, plus a monthly subscription of $99 for up to $150,000 a year in processing, $139 up to $250,000, and $199 and up beyond that. You pay interchange on top of all of it.