What happens when you tap your phone to pay?

A truck stop in North Dakota went to court over 21 cents

Ruling filed October 26, 2026

A truck stop and convenience store sued over a fee no customer ever sees on a receipt. The case reached a federal appeals court, which is a long way to carry 21 cents.

The 21 cents is the base of a US cap on what big banks can collect from the shop's side when you pay by debit card. A court struck down the cap on October 26, 2026, but it still applies for now. The court set no new number. It told the Fed to write a new rule. Source

You never see this fee, and who really ends up bearing it is still argued about. To see why anyone would fight over it, follow the money.

It starts with a very short radio

Your phone talks to the shop's terminal over NFC, a radio that runs at 13.56 MHz. The standards group gives a typical range of up to 2 cm. It certified devices at 5 mm for years, and since October 2025 its tests can reach 2 cm. That's why you have to hold it so close. Source Source Payment readers have their own test rules, which reach 4 cm. Source

The phone acts like a contactless card. That's why one terminal can take a card, an iPhone and an Android phone without caring which is which. The terminal sends a command, the phone replies, and they take turns. Source

A tap is not always a phone. About 4 in 10 US in-person card payments were contactless in 2024, and a tapped plastic card counts. Data In a separate survey of US adults, phones were 11% of in-person payments. Source

Your phone doesn't send your card number

It sends a stand-in called a device token: a card number for one wallet on one device. Source With plastic, the shop gets the printed number. With a wallet, the shop never gets the real one. Source

That pays off when something goes wrong. If you lose the phone, the bank can suspend that one token without replacing your plastic card. Source

On an iPhone, the token and keys sit in a certified security chip and never on Apple's servers. Source Android allows two designs, a chip or an ordinary app, so it varies by phone. Source

Then it signs a code that only works once

Each payment comes with a one-time code, computed from a key and a counter that goes up with every payment. The key is loaded when you add the card, and your bank or the network holds it too. Source The code is valid only for its own transaction, so it can't be reused in another one. Source

A comparison, and only a comparison: a magnetic stripe is like showing the same ID card every time. The code is like a new note for each purchase, signed with a pen only you and your bank hold.

No system is perfect. Security researchers have published design flaws in how contactless pieces fit together. Source

Your tap makes a round trip

1. Your phone
2. The shop's terminal
3. The shop's processor
4. The card network, which turns the token back into your real number
5. Your bank or card company, which says yes or no

The answer comes back the same way. Your bank checks the card, then whether the account is open and can cover it, with fraud controls along the way. Source

Visa and Mastercard are not your bank. Neither one issues cards or lends money. American Express is different: it does both. Source Visa's rules give a US bank 10 seconds to answer, and then Visa answers for it. Source We could not find a measured time for the whole trip. In Israel, a national switch called SHVA sits between terminals and card companies. Source

And no money has moved yet

Card payments happen in three stages.

• Authorization: your bank says yes and places a hold.
• Clearing: the banks exchange information about the sale.
• Settlement: the banks exchange money.

A 2007 Mastercard diagram shows clearing usually within a day and settlement usually within two. Those are old numbers, and we could not find a current official count. Source

Settlement doesn't happen one coffee at a time, either. Each bank's activity gets added up into one lump sum. Source By the time you reach the door, your coffee has been approved, not paid for.

Follow the money yourself

US, Visa, in person. A processor is the company that handles card payments for a shop. This shop pays Square's list price, a flat rate for any card. Everything here is arithmetic from published price lists, using Visa's ordinary in-person rows so $10 and $100 run on one formula. Restaurants, supermarkets and very small shops have other rows. So do small sales, and a $10 sale may count as one. Source

What the court actually said

The cap is 21 cents, plus 0.05% of the sale, Source plus 1 cent for banks that meet fraud standards. Source It covers banks with at least $10 billion in assets. Source

The law tells the Fed to consider the extra cost of a particular transaction. Picture a lemonade stand: the lemons in your cup are an extra cost, and the stand itself is a fixed one. The court said fixed costs can't count, and that the Fed's job is "not just pick a number and hope it is close enough for government work." Source

Bank groups say banks, credit unions and consumers will pay for this. Source Retailers applauded. One analyst guesses a new cap could be under 5 cents, and that is only a guess. Source Check back: the court's order hasn't taken effect yet.

Who pays for card rewards?

Card rewards reached $47.5 billion in the US in 2024. The fee shops pay is one source of that money. Source Source

Shops usually charge one price whatever you pay with. So in a model by researchers at the Federal Reserve and the Bank of Canada, using US data from about 2018, people paying with debit and cash help cover credit card rewards. Rewards came to 0.70% of purchases for the highest-income group and about 0.25% for the two lowest. Source The amounts change with the model's assumptions, and people still argue about them.

We explain how the system works. We don't tell anyone which card to get or what to buy.

What does a tap actually prove?

On a phone, it usually proves someone passed that device's check, like a face or a passcode. Some setups, like transit modes, can skip it. It doesn't prove who you legally are. Anyone whose face or passcode works looks the same to the bank. Source A plastic card under the limit proves only that someone is holding it. Israel's limit is NIS 300. Source We could not find a published US figure.

Is it safer? We can't tell you. In the UK in the first half of 2025, contactless cards ran at 1.2p of fraud per £100 spent, against 6.9p for all card fraud. But that 6.9p includes online, phone and mail fraud, about 72% of UK card fraud losses in that half-year, and a tap can't be used for those. Source We found no rate for phones alone, and none at all for the US or Israel.

Build the calculator

• You will have Your own table that takes any price and shows what each party gets, and a graph of how the cut changes.
• Time About 45 minutes.
• You need Paper and a calculator, or LibreOffice Calc (free, no account). No card, purchase or bank account.

1. Make one row per card, using these rates from Visa's sheet: rewards credit 1.65% + 10¢, premium credit 2.30% + 10¢, big-bank debit 0.05% + 22¢, small-bank debit 0.80% + 15¢.
2. Add the shop's total, using Square's list price: 2.6% + 15¢.
3. Add the network's two main fees, about 3¢ at $10 and about 15¢ at $100. The rates are in this bank's schedule.
4. Find the price where small-bank debit passes big-bank debit. You should land near $9.33.
5. Graph the bank's share of the price from $1 to $100 for each card. Which line falls fastest? Why?
6. Type in your own guess for a new cap, and see who gains on this flat-price plan. Be careful: the shop's bill doesn't change.

Want more?

With a parent or teacher aware, ask a neighborhood shop owner roughly what card companies take in total. Only ask for a rough percent, never statements or customer details, and it's fine if they say no. Work out a day, a month and a year, then turn it into what the shop sells: how many falafels is that? Outside the US, stick to what the owner tells you, because these rates are US only.

Back at the counter

Tomorrow you will buy something small. The phone will buzz, and you'll already be turning toward the door. The receipt will say $10.

It won't mention the truck stop.

Back to the Lab

Last checked November 4, 2026. The debit cap case is moving, so these numbers may change. Torah Tech researched and wrote this lesson with the help of Claude, an AI made by Anthropic. Any mistakes are ours.