Which number do all Discover Cards start with?

Discover Cards start with the number 6. This is part of a numbering system used for payment cards, where the first digit is a significant identifier of the card network. For example, Visa cards begin with a 4, MasterCard cards primarily start with a 5, and American Express cards typically start with 3. Discover, being its own payment network, uses 6 as its starting digit, which differentiates it from other major card networks. This standardized system helps merchants and processing systems easily recognize the type of card being used for transactions.