A card machine does not charge you anything per transaction. The company behind it does, and that charge has two parts which behave completely differently.
One part is a percentage. It rises and falls with the size of the sale. The other part is a flat amount in pence, charged once per authorisation, and it does not care whether the sale was £3 or £300. Most quotes lead with the percentage and bury the pence, which is why two providers can look almost identical on the headline and land a long way apart on your statement.
Which of the two hurts you more is not a matter of opinion. It is decided by your average sale.
The percentage has a wholesale floor underneath it. Interchange, the slice that goes to the bank that issued the customer's card, is capped by law in the UK at 0.2 per cent on consumer debit and 0.3 per cent on consumer credit under the Interchange Fee Regulation. Nobody can sell you a percentage below that floor on those cards, and we have been through the rest of that stack in an earlier piece on what sits under the headline rate.
The pence part is different. It is the provider's own charge for processing the authorisation, and it is set by the provider rather than by any cap. Merchant Savvy's comparison of UK acquirers lists an authorisation fee of 4.5p at Worldpay and Barclaycard, 4p at Elavon and Global Payments, 3.25p at Clover and 0p at Square. Same job, same card, and a spread of 4.5p between the top and the bottom of that list.
4.5p sounds like nothing. Whether it is nothing depends entirely on the next number.
UK Finance publishes the national figures every month. In its October 2025 update there were 2.3 billion debit card transactions worth £67.1 billion, and 403 million credit card transactions worth £22 billion.
Divide one by the other and the average UK debit card sale is £29.17. The average credit card sale is £54.59. Those are national averages across every sector, and your own number is almost certainly nowhere near them.
Run a 4.5p authorisation fee against three realistic sales:
Identical fee in pence. Wildly different fee in proportion. A coffee shop and a restaurant can sign the same contract and experience it as two different prices.
SumUp publishes 1.69 per cent on its pay as you go plan. Square publishes 1.75 per cent for in person transactions with UK cards. Zettle publishes 1.75 per cent. On the surface, 6 hundredths of a percentage point separates them.
On a £29.17 sale, 1.75 per cent is 51.05p and 1.69 per cent is 49.30p. The gap between the two headline rates is 1.75p a sale.
A 4.5p authorisation fee is more than twice that gap. So a quote with the better percentage and a per item fee attached can be the more expensive quote, on exactly the kind of sale most venues actually take. The percentage is the number everybody argues about. The pence is the number that quietly decides it.
Fixed fees are not only an acquiring thing, and they are not always charged per item.
Square's in person price carries no fixed fee, but its online price for UK cards is 1.4 per cent plus 25p. On a £10 collection order, that 25p is 2.5 per cent of the sale sitting on top of the 1.4 per cent. Small online baskets are the worst possible shape for a fixed fee, and takeaway menus are full of them.
SumUp's alternative plan moves the fixed cost from the transaction to the month: 0.99 per cent at £19 a month. The saving against its own 1.69 per cent plan is 0.7 percentage points, so the £19 pays for itself at £19 divided by 0.007, which is £2,714.29 of card turnover a month. Below that, the cheaper percentage costs you more.
Every fixed charge works this way. It converts into a percentage only once you know the volume it is spread across, and nobody quoting you can know that number. You can.
It does nothing about your card mix. Commercial cards, corporate cards and cards issued outside the UK sit outside those interchange caps entirely, and on a hotel or a conference venue they can move the bill more than any per item fee ever will. That is a different argument, and it is the one about whether your statement is on interchange plus or blended pricing.
It does nothing about the fees that are not per transaction at all: PCI charges, terminal costs, and whatever non usage terms sit in the contract you are being asked to sign. Free hardware does not touch them either, as we set out when we went through what the word free is actually covering.
And if your average sale is large, this whole exercise is close to a rounding error. At £65 a head the percentage is where your money goes, and counting pence per item is effort better spent elsewhere. This matters most to sites taking a high count of small sales: cafes, bars, quick service counters, anywhere the queue is long and the basket is short.
Do those four and two quotes stop being a beauty contest between percentages.
The technology is Shift4's.
We do charge an authorisation fee, priced per contract. We say so because the arithmetic above applies to us the same as to anyone else, and you should run it on our quote too. We do not charge a PCI fee, terminal rental or a subscription on the terminal, and hardware, setup and upfront cost are free. There are terms in any contract that do not appear on a website, ours included, and you should ask for them in writing before you sign.
If you want to see what your own numbers do to a quote, the savings calculator on our pricing page works off your card takings rather than a headline percentage.
How much do card machines charge per transaction?
There is no single number, because the charge is a percentage plus any fixed amount per authorisation. Published UK rates for in person sales run from 1.69 per cent on SumUp's pay as you go plan to 1.75 per cent at Square and Zettle, and separately listed authorisation fees run from 0p to 4.5p depending on the acquirer.
Does every card reader charge per transaction?
No. Some published price lists carry a percentage only on in person sales with no fixed amount per item, and Square's in person UK pricing is one of them. Others add an authorisation fee on every authorisation. The only way to know is to ask for the per item line by name.
How much does Visa charge merchants in the UK?
Visa does not bill the merchant directly. Part of what you pay is interchange, which goes to the bank that issued the customer's card and is capped in the UK at 0.2 per cent on consumer debit and 0.3 per cent on consumer credit. Scheme fees and your provider's own margin sit on top of that, which is why your all in rate is always higher than the cap.
Send three months of card statements and one busy Friday. We will show you what your card processing is costing you now against what it would cost with us, with every fee named, before you commit to anything.
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