For a service business that bills by invoice and payment link, interchange plus (where you pay the real card cost plus a disclosed markup) with an ACH option on every invoice, and no extra fee just for sending an invoice, is the setup to compare against flat rate. In NPS’s study, a model finds the invoice channel shows the largest savings of any channel. Flat-rate providers often charge a higher price for invoices than for in-person sales and add an invoicing fee on top. This guide shows what that costs on a $150 and a $300 invoice, what the study found for the invoice channel, which fees to look for, and when flat rate is still the better choice.
The short answer
- Invoices cost more than counter sales on flat rate. Square charges 3.3% plus 30 cents for invoices against 2.6% plus 15 cents in person, and Stripe Invoicing adds 0.4% per paid invoice, per Stripe’s own pricing page (read November 13, 2026).
- In NPS’s 2026 pricing study, a model finds invoice payments show the largest savings of any channel on pass-through pricing, 19% to 31% across tickets from $15 to $2,500.
- The study is a model by a processor that sells pass-through pricing, so test it on your own invoices.
- ACH, a bank-to-bank payment, is often cheaper than a card for a larger invoice.
- Flat rate can still be cheaper for a very new business with very low volume.
What an invoice costs on a flat-rate provider
A flat-rate provider charges one price for most card payments, but not the same price for every way you collect. NPS’s 2026 pricing study quotes the published prices of the two largest flat-rate providers, accessed in October 2026. Square charges 3.3% plus 30 cents for online payments and invoices, compared with 2.6% plus 15 cents for in-person payments on its Square Free plan. Stripe charges 2.9% plus 30 cents for card processing, and its Invoicing fee adds 0.4% per paid invoice. Stripe also adds 0.5% for manually entered cards, which matters when a customer calls in a card number. Square’s keyed or card-on-file price is 3.5% plus 15 cents.
Here is the arithmetic on two common invoice sizes at 3.3% plus 30 cents, which is Square’s invoice price and also the study’s flat-rate benchmark for invoices. A $150 invoice costs $5.25. A $300 invoice costs $10.20. A business that sends 100 invoices of $150 in a month collects $15,000 and pays $525 in card fees at that price. These are plain arithmetic on the quoted prices. They leave out disputes, instant payouts and other add-ons.
Invoice fees today
What invoices cost on flat rate
- $150 invoice$5.25Square invoice fee3.3% plus 30 cents, Square’s invoice price and the study’s flat-rate benchmark for invoices
- $300 invoice$10.20Square invoice fee100 invoices of $150 in a month = $525 in card fees on $15,000 collected
The point is that sending an invoice, or a payment link, is a different kind of payment from a counter sale. The customer is not standing in front of you, the card is not swiped or tapped. In the prices the study quotes, Square charges 3.3% + 30 cents for invoices against 2.6% + 15 cents in person, and Stripe adds 0.4% for Invoicing (per Stripe’s own page, read November 13, 2026).
What interchange plus changes for invoices
Interchange plus separates the costs inside the price. You pay the interchange fee that goes to the bank that issued the customer’s card, the card networks’ assessments, and one markup stated in your agreement. NPS explains the model, and the other common ones, in its guide to merchant account pricing models. A cheaper card costs you less, and a pricier card costs you more.
Under federal rules (the Durbin Amendment, put into effect as Regulation II), interchange on debit cards from large banks is capped at 0.05% of the sale plus 21 cents, with a 1 cent fraud adjustment. A flat rate charges the full percentage on that card anyway. Be careful with the word “most.” The cap covers debit cards from large banks. Debit cards from smaller banks are exempt and cost more, and the study’s model assumes 35% of debit volume comes from exempt issuers. The Federal Reserve has proposed lowering the cap, which the study calls unresolved.
Business cards are the other side. They tend to cost more in interchange, and the study says that narrows the gap for B2B invoices. If your customers are consumers, a large share of them will pay with personal debit and credit cards. If your customers are businesses, more of them will use company cards. Know which you serve before you estimate savings.
What the study found for the invoice channel
The study is “The Flat-Rate Tax,” by Allen Kopelman, the CEO of NPS. It is a cost model built on published rate schedules, not a survey, and it was written by a processor that sells pass-through pricing. Read it as a reason to ask for a quote, not as proof of your savings. Link: NPS’s 2026 pricing study.
Invoices and payment links are one of the three channels it models. The study says businesses selling online or by invoice pay 19% to 31% less in processing costs on pass-through than on flat rate, across average tickets from $15 to $2,500, and that invoice payments show the largest savings of any channel. Its example: a business collecting $50,000 a month through invoices at a $150 average ticket keeps about $6,100 a year by moving from flat rate to pass-through.
The model also leaves out chargeback fees, instant payout fees and other add-ons on the flat-rate side, so the real flat-rate bill can be higher than the model shows. It treats NPS’s markup as an input, not a price list, and it reports that NPS does not charge an add-on fee for invoices and payment links beyond the same markup as any other transaction. Treat that as NPS’s statement about its own offer and ask for it in writing.
How the debit mix changes with the size of the invoice
The study uses a debit share that falls as the ticket rises: 25% at $150, 22% at $300, 15% at $1,000 and 10% at $2,500, which it says come from NPS merchant experience. Smaller invoices have more debit, so a flat rate overcharges a bigger share of them. Larger invoices have more credit, and more business cards.
Debit mix by ticket
Debit share falls as invoice size rises
| Average ticket | Debit share | What that means |
|---|---|---|
| $150 | 25% | More debit, flat rate overcharges a bigger share |
| $300 | 22% | Still mostly consumer debit and credit |
| $1,000 | 15% | More credit and business cards |
| $2,500 | 10% | More business cards; Level 2/3 data matters |
For a service business, that means the savings pattern depends on what you bill. A house cleaner, a tutor or a dog groomer with $75 to $200 invoices paid by individuals will see a lot of debit. A consulting firm or a contractor sending $5,000 invoices to companies will see more credit and commercial cards, and will care about Level 2 and Level 3 data, extra transaction details that can lower the cost of business cards. NPS explains them in its guide to Level 2 and Level 3 processing.
Younger customers pay with debit more often, the study says, and young businesses often pay invoices with a business debit card because they do not yet have a company credit card. Ask your provider for a report of paid invoices by card type, or look at your dashboard export, so you can see your own mix.
ACH, deposits and getting paid faster
A card is not the only way to pay an invoice. ACH is a bank-to-bank transfer, and NPS’s ACH guide says optimized ACH is often in the range of 0.50% to 1% with a cap, compared with 2.5% to 3.5% for credit cards on its page. NPS also says ACH has fewer chargebacks because it does not follow card-network dispute rules. On a $2,000 job, the difference between a card fee and an ACH fee in those ranges is easily worth a line on the invoice that says “pay by bank transfer.” Read the ACH optimization guide for the details, and get the exact ACH price in writing.
Speed matters as much as cost. NPS says businesses are paid in eight days or less when they can pay through a secure link. Its software supports email and text payment requests, QR codes for printed invoices and quotes, recurring billing, split payments and deposits for project work. Whatever you choose, make sure the customer can pay in one or two taps on a phone, because an invoice that is hard to pay waits longer.
If you want customers to pay by ACH instead of a card, you can offer a discount or show a lower price for bank payment. NPS describes the idea in its guide to dual pricing. The rules for adding a fee or giving a discount for card payers differ and can create problems with the card networks if done wrong, so set it up with a provider that explains them.
The features that matter besides the rate
A service business does not run on a rate. It runs on getting invoices out, getting paid and closing the books. Compare the workflow:
- Branded invoices and payment links with your logo and colors, so the customer sees your business and not the processor.
- Automatic reminders, early-pay discounts and late-fee rules.
- A customer portal where people can see their history and receipts.
- Partial and recurring payments for deposits, retainers and subscriptions.
- Two-way accounting sync, so an invoice created in QuickBooks Online or in the payment tool shows up in both and settles correctly.
- Roles and permissions, so staff can send invoices without seeing bank or financial data.
- Whether the price depends on the number of users.
Invoicing workflow
Features to compare beyond the rate
- Branded invoices and payment links with your logo and colors
- Automatic reminders, early-pay discounts and late-fee rules
- A customer portal where people can see their history and receipts
- Partial and recurring payments for deposits, retainers and subscriptions
- Two-way accounting sync with QuickBooks Online or your payment tool
- Roles and permissions so staff can send invoices without seeing financial data
NPS describes Smart Invoicing as covering these items, with unlimited users. See what smart invoicing is and NPS1 and Smart Invoicing with QuickBooks.
When flat rate is still the better choice
The study says plainly that flat rate is sometimes the better deal. It names in-person businesses with very small tickets, around $15 and under, and brand-new businesses with very low volume. A service business sending a handful of invoices a month is closer to the second group than the first.
NPS’s pricing guide lists flat rate as best for startups and merchants processing under $10,000 a month, and interchange plus as best for businesses processing over $25,000 a month. A business sending $1,500 in invoices a month has little to gain in dollars from a change, and a flat-rate account with no monthly fee and no contract is fine.
There is also a case for flat rate when your invoicing tool is built into your accounting software and the two work well together. If you use QuickBooks Payments, for example, read QuickBooks’ current pricing page, note which fees apply to invoices, ACH and card-on-file, and compare the total with a quote. We do not quote QuickBooks prices here, because they change.
How to get a fair quote
Gather three months of paid invoices: number, total, average, share paid by card versus ACH, and card types if you can see them. NPS says its statement review is free. See how much you are really paying on Stripe, Square, PayPal or QuickBooks.
Ask each provider to price that exact set in dollars, with all fees included. Then ask:
- What is your markup, as a percentage and per transaction, and is it the same for invoices as for counter sales?
- Is there any extra fee for sending an invoice, creating a payment link or keying in a card?
- What are your ACH fees, and is there a cap?
- What monthly, gateway, PCI and software fees apply?
- What do you charge for a dispute, and do you return it if I win?
- Is there a contract term or early termination fee?
- Who answers the phone when a customer says the link will not work?
Compare the effective rate (total fees divided by total card sales) and the dollars a year. If a provider will not do the math on your own invoices, or will not put the markup in writing, treat that as information.
Getting a fair quote
What to ask every provider before you switch
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Markup rateWhat is your markup, as a percentage and per transaction, and is it the same for invoices as for counter sales?
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Invoice or link feesIs there any extra fee for sending an invoice, creating a payment link or keying in a card?
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ACH feesWhat are your ACH fees, and is there a cap?
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Monthly and gateway feesWhat monthly, gateway, PCI and software fees apply?
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Dispute chargesWhat do you charge for a dispute, and do you return it if I win?
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Contract termsIs there a contract term or early termination fee?
For the full picture across every sales channel and average ticket, read our guide to cheapest payment processing in 2026.
Who wrote this, and where NPS fits
Nationwide Payment Systems (NPS) publishes this guide. We are a payments company based in Fort Lauderdale, Florida, in business since 2001, and we sell merchant accounts and invoicing software, so we are not neutral. We offer interchange-plus pricing, ACH, a payment gateway and Smart Invoicing, and we also offer flat-rate options. We do not publish a price list, because pricing depends on volume, invoice size, card mix and risk. The study we cite was written by our CEO. Browse more in our payments guides or see where Stripe fees actually go.
We are not the right fit for every business. If you send only a few invoices a month, want to start today with no application, or your accounting software already handles payments well, a simpler setup may cost you less.
Bottom line
For a service business using invoices and payment links, interchange plus with an ACH option on every invoice and no extra fee for the invoice itself is the setup to compare against flat rate. On flat rate, an invoice often costs more than a counter sale, and in NPS’s study, a model finds the invoice channel shows the largest savings of any channel. The study also says flat rate can win for very low volume or very new businesses. Ask for a quote built from your own paid invoices, and compare every fee. If you would like a second opinion on a quote or on your current statement, you can contact our team, and if staying where you are is the better answer, we will say so.
Frequently asked questions
What do invoices cost on Square or Stripe?
In NPS’s 2026 pricing study, Square charges 3.3% plus 30 cents for invoices, and Stripe’s Invoicing fee adds 0.4% per paid invoice on top of its card price. These are from published pricing accessed October 2026.
Is interchange plus cheaper for invoices?
Often. In the study, a model finds invoice payments show the largest savings of any channel, 19% to 31% across tickets from $15 to $2,500. It is a model from a processor that sells pass-through pricing, so test it on your own invoices.
How much could I save per year?
The study gives one example: $50,000 a month through invoices at a $150 average ticket keeps about $6,100 a year in the model. Your result depends on your card mix and fees, so ask for a quote.
Should I offer ACH on invoices?
Often yes. NPS’s guide says optimized ACH is often 0.50% to 1% with a cap and has fewer chargebacks. Offer cards as well, since some customers prefer them.
When is flat rate better for a service business?
The study says flat rate can be better for brand-new businesses with very low volume. NPS’s pricing guide lists it as best for merchants under about $10,000 a month.
Does the debit cap apply to every debit card?
No. The cap applies to debit cards from large banks. Debit cards from smaller banks are exempt and cost more.
Does NPS review my current statement for free?
Yes. NPS offers a free statement review. Send a recent statement and ask for the math on your own invoices.
