How to Read a Credit Card Number
Published: October 20, 2026 · By Marcus Hale
A credit card number (PAN) is structured into four fields: MII, BIN, account number and check digit. Here's how to read each.
MII (Major Industry Identifier)
The first digit identifies the industry. 4 = banking (Visa), 5 = banking (Mastercard), 3 = travel (AMEX), 6 = merchandising (Discover).
BIN (Bank Identification Number)
Digits 1-6 identify the issuing bank, brand, card level and country. Use the BIN Lookup tool.
Account number
Digits 7 to n-1 are the issuer-assigned account identifier. Length varies by brand.
Check digit
The last digit is the Luhn checksum. Use the Luhn Checker to validate.
Worked example
Take 4242 4242 4242 4242. The first digit 4 identifies the banking industry and the Visa network. The first six digits 424242 are the BIN, which maps to a test Visa range. The next digits up to the last are the account identifier assigned by the issuer. The final digit is the Luhn check digit that makes the whole number valid.
Why the structure matters
The structure lets systems validate a number before contacting an issuer. Length rules by brand, prefix rules by network and the Luhn check digit together reject most malformed input. That reduces wasted authorization attempts and improves the reliability of checkout forms.
Reading a number safely
Only the first six digits are needed to identify the issuer. Never paste a full card number into a third-party tool. For development, use published test numbers rather than real card data. This site provides a test-card generator for exactly that purpose.