How do credit card numbers work?

Each card number contains embedded information that identifies the card network, issuing bank, and includes a check digit for validation. The first few digits, known as the Issuer Identification Number (IIN) or Bank Identification Number (BIN), determine the card type and issuing institution.

Different card networks use distinct numbering patterns. Visa cards start with 4, Mastercard with 51-55 or 2221-2720, American Express with 34 or 37, and Discover with 6011, 644-649, or 65. These patterns allow payment systems to instantly route transactions to the correct network before any verification occurs.

The final digit of every card number is a check digit calculated using the Luhn algorithm. This mathematical formula catches common transcription errors like single-digit mistakes or adjacent digit transpositions, providing a first layer of validation before contacting payment processors.

Tool description

This tool identifies credit card types from partial or complete card numbers. Enter any portion of a card number and instantly see which payment networks it could belong to, along with detailed specifications for each match including valid card lengths and security code requirements.

Examples

Input Detected Type Card Lengths
4 Visa 16, 18, 19
51 Mastercard 16
34 American Express 15
6011 Discover 16, 19
35 JCB 16, 17, 18, 19
30 Diners Club 14, 16, 19

Features

  • Real-time detection — Card type identified as you type, even from just the first digit
  • Multi-match support — Shows all possible card types when the prefix matches multiple networks
  • Security code info — Displays the security code name (CVV, CVC, CID) and length for each card type
  • Card network logos — Visual icons for major card brands including Visa, Mastercard, Amex, Discover, JCB, and Diners Club
  • Input formatting — Accepts card numbers with or without spaces for easy pasting

Use cases

  • E-commerce development — Test payment form validation logic by checking how different card prefixes are detected
  • Customer support — Quickly identify a customer's card network from partial card information to route inquiries correctly
  • Educational purposes — Learn how card numbering schemes work and understand the structure of different payment networks

How it works

The tool uses the IIN/BIN prefix matching system. When you enter digits, it compares them against known patterns for all major card networks. Since different networks use unique starting sequences, even a single digit can narrow down or identify the card type. As more digits are entered, the matches become more precise until a single card type remains.

Supported card networks

Network Prefix Pattern Typical Length
Visa 4 16
Mastercard 51-55, 2221-2720 16
American Express 34, 37 15
Discover 6011, 644-649, 65 16, 19
JCB 3528-3589 16-19
Diners Club 300-305, 36, 38-39 14-19
Maestro 5018, 5020, 5038, 6304 12-19
UnionPay 62 16-19

FAQ

Is it safe to enter my real card number? All processing happens locally in your browser. No card data is transmitted to any server. However, for security best practices, avoid entering complete real card numbers unless necessary.

Why does my card show multiple matches? Some card prefixes overlap between networks, especially with just a few digits entered. As you type more digits, the matches narrow down to the correct network.

What is the security code called on different cards? Visa and Mastercard use CVV (Card Verification Value), American Express uses CID (Card Identification Number), and Discover uses CVV. The tool shows the correct name for each card type.