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A credit card number is composed of several parts: the issuer identification number (IIN), the individual account number, and the check digit. The IIN is the first six digits of the credit card number, and it identifies the issuer of the card. The individual account number is usually up to 12 digits long, and it identifies the specific cardholder account. The check digit is the last digit of the credit card number, and it helps to verify that the credit card number is valid.
The Length of a Credit Card Number
Most credit card numbers are 16 digits long. The number is displayed in four groups of four digits, separated by dashes, like this: 1234-5678-9012-3456. Some credit card companies use a slightly different format, with four groups of four digits separated by spaces, like this: 1234 5678 9012 3456.
The last four digits of the credit card number are the “check digit.” The check digit is used to verify that the credit card number is genuine. To calculate the check digit, multiply eachdigit in the number by 2, starting with the first digit (the right-most digit). If any of the products are two digits long (i.e., greater than 9), add the digits together to get a single-digit number (this is called “reducing” a two-digit number to a single digit). Add all of these numbers together. The last digit of this sum is the check digit.
So, if our example credit card number is 1234 5678 9012 3456, we would calculate the check digit like this:
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
2 (1+2) 4 (3+4) 6 (5+6) 8 (7+8) 0 (9+0) 2 (1+2) 4 (3+4) 6 = 70
7 + 0 = 7
Therefore, the check digit must be 7.
The Number of Digits in a Credit Card Number
The number of digits in a credit card number can vary depending on the type of card. The table below outlines how many digits are in each type of credit card.
Type of Credit CardNumber of Digits
The Check Digit in a Credit Card Number
American Express, Discover, MasterCard, and Visa all use the following algorithm to generate the check digit. The final digit of a credit card number is the check digit. The check digit is generated by adding together the digits of the credit card number starting with the right-most digit and moving to the left. Starting from this sum, take every seconddigit (counting from right to left) and add these digits together. For example, for a MasterCard number 4485 0320 9095 5 Twist it around so that it’s 5995 0304 8458 4
Start at the rightmost digit and add every other digit to it: 5 + 0 + 0 + 9 + 3 + 8 = 25
Now take this sum (25) and add all of *its* digits together: 2 + 5 = 7
This final sum (7) is your check digit! So your full credit card number should be 4485 0320 9095 5 7
From personal experience, I would say that the average credit card has between 16 and 20 numbers. However, there are some credit cards that have as few as 12 numbers and some that have as many as 22. The number of digits in a credit card depends on the issuing bank and the type of credit card.