What is the credit card number on American Express (AMEX)?

10 Mar 2023

AmEx account numbers are embossed, 15 digits long, and spaced in three blocks of four, six, and five digits from left to right: "3xxx xxxxxx xxxxx". It is yet another distinct AmEx security feature. On the contrary, Visa, MasterCard, and Discover numbers are all 16 digits long and divided into four groups of four digits each.

The American Express card number format adheres to the rules established by the American National Standards Institute (ANSI). For all networks, the IIN is always the first six digits of the card number, as shown in the image to the right.

The Luhn algorithm (also known as the Luhn formula or the "modulus 10" or "mod 10" algorithm) validates AmEx card numbers and most other credit card numbers. It is a simple procedure that verifies the card number as follows:

The formula involves doubling the value of every other digit, starting with the check digit on the rightmost side and moving left. It doesn't matter which direction you begin since AmEx numbers consist of odd-numbered digits. If the sum of the doubled digits is greater than nine, add the digits of the resulting sum. For instance, 5 x 2 = 10 would become 1 + 0 = 1, or 18 would become 1 + 8 = 9.

Add up all the generated digits, including the odd ones you didn't double. If the resulting sum is zero, the card number follows the Luhn formula and is valid. The card number will be invalid if it is greater than zero.

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