How a Card Payment Actually Works

You tap your card. The terminal beeps. The cashier hands you a receipt. The whole thing takes under two seconds.

Behind that two seconds is a chain of encrypted messages, risk calculations, and financial settlements passing through five different organisations across multiple continents. It's one of the most sophisticated real-time transaction networks ever built, and it underpins trillions of pounds of commerce every year.

Here's exactly what happens.

The Five Parties in Every Card Transaction

Before we trace the journey, you need to know who's involved:

The Customer holds a card issued by their bank. Every time they pay, they're borrowing that card's identity from their bank.

The Merchant accepts the payment through a terminal provided by their acquirer.

The Acquirer (also called the merchant bank) is the financial institution that processes card payments on behalf of the merchant. Teya is an acquirer.

The Card Scheme (Visa, Mastercard, American Express) is the network that connects acquirers and issuers. They don't hold money. They route messages and set the rules.

The Issuer is the customer's bank. Lloyds, Barclays, Monzo, HSBC. They issued the card and they decide whether to approve or decline the transaction.

Step 1: Card Presented (0.0 seconds)

The customer taps their card or phone on the terminal. A contactless chip sends an encrypted token over NFC (Near Field Communication) at a range of roughly 4cm. This token contains a one-time cryptogram tied to the transaction amount and a unique counter. It cannot be reused. Even if intercepted, it's worthless.

For chip-and-PIN, the process is identical except the PIN is verified locally on the terminal.

Magstripe transactions (rare now) are significantly less secure and carry higher interchange rates as a result.

Step 2: Authorisation Request (0.1 to 0.3 seconds)

The terminal packages the transaction into an ISO 8583 message, a standard format used across the global payments network. This message contains the card number (tokenised), the amount, the merchant ID, the terminal ID, and a cryptographic signature.

The terminal sends this to the acquirer over a secure encrypted connection.

The acquirer receives it, validates the merchant account, checks the message format, and runs it through fraud rules: Is this merchant active? Is the amount within expected ranges? Has this terminal been flagged?

If everything checks out, the acquirer forwards the request to the appropriate card scheme.

Step 3: Scheme Routing (0.3 to 0.6 seconds)

Visa and Mastercard operate some of the world's most resilient networks. VisaNet alone processes over 65,000 transactions per second at peak capacity with 99.999% availability.

The scheme receives the authorisation request and routes it to the correct issuing bank based on the first six digits of the card number (the Bank Identification Number, or BIN). The scheme also logs the interchange fee due, which will be collected during settlement later.

It takes typically 50 to 100 milliseconds for a message to travel from a UK acquirer to the scheme network and out to the issuing bank.

Step 4: Issuer Decision (0.5 to 1.5 seconds)

This is where the magic happens. The customer's bank receives the transaction request and runs dozens of checks in milliseconds:

Funds check. Does the cardholder have sufficient balance or credit available?

Fraud scoring. The issuer's fraud model scores this transaction. Is it consistent with the cardholder's usual behaviour? Is the merchant category expected? Is it the right location and time? Banks process hundreds of variables in real time using machine learning models trained on millions of transactions.

3DS (3D Secure). For online transactions, the issuer may trigger a 3DS challenge, requiring the cardholder to verify via their banking app. For contactless in-person payments, this step is usually bypassed.

Velocity checks. Has this card been used multiple times in the last few minutes? Is the amount unusually high?

The issuer sends back a response code. 00 means approved. Anything else is a decline, with specific codes for "insufficient funds", "card blocked", "suspected fraud", "do not honour", and so on.

Step 5: Response Returns and Terminal Updates (1.5 to 3 seconds)

The response travels back through the same chain in reverse: Issuer to Scheme to Acquirer to Terminal.

The terminal receives the response and displays "Approved" or "Declined". If approved, it prints or displays a receipt.

The whole journey, door to door, is typically 1.5 to 3 seconds for a contactless in-person transaction. Online card transactions may take slightly longer due to 3DS flows.

After the Transaction: Settlement

The authorisation is not the payment. It's a hold.

At the end of each business day, merchants batch their transactions and send them to the acquirer. The acquirer sends the batch to the card scheme. The scheme nets out what's owed between all acquirers and issuers, and settlement occurs through central banking systems.

The merchant receives the funds minus fees, net of interchange and the acquirer's margin.

With Teya, the default is next-day settlement, meaning the funds are in your account the next business day. This is faster than many traditional providers who settle in 2-3 days.

The Fees That Flow Through This Chain

Every step in the chain has a cost:

Interchange fee: Set by Visa or Mastercard. Paid to the issuing bank. The biggest component of your processing cost. Ranges from around 0.2% for a standard consumer debit card to over 1.5% for a premium rewards credit card. Teya blends these into a single flat rate.

Scheme fee (assessment): A small levy from Visa or Mastercard, typically 0.1% to 0.2%. Charged to the acquirer, usually passed on to you.

Acquirer margin: Teya's fee for providing terminals, fraud monitoring, settlement, support, and compliance. This is the part you negotiate.

Traditional providers separate all of these out and bill you line by line, making it nearly impossible to understand your real cost. Teya bundles them into a single blended rate so you always know what you're paying.

Why Any of This Matters to You

Understanding the mechanics of card processing matters because it shows you where the cost comes from and where you have leverage.

You cannot negotiate interchange. It is fixed by Visa and Mastercard based on your card mix: debit vs credit, consumer vs commercial, UK domestic vs foreign-issued. If 40% of your customers pay with premium rewards cards, your interchange cost is structurally higher than a business where 80% pay with basic debit cards.

What you can negotiate is the acquirer margin. A transparent acquirer like Teya shows you the blended rate. An opaque one buries the interchange in a confusing statement and adds markup on top.

Use our calculator to upload your last statement. We'll calculate your real blended rate and show you exactly what switching to Teya would save you.