ACCOUNT NUMBER VERIFICATION
CHECK DIGIT SCHEME

By David Leppek
Pay By Touch Merchant Services

The Luhn Mod-10 Method is an international standard for validating card account numbers. Previously this had been documented by ISO 2894/ANSI 4.13 which was created in 1980 and since retired. Currently this is number scheme is defined by JTC 1/SC 17. Such account numbers, which cannot exceed 19 digits including the check digit, are assigned, embossed and encoded to include a single check digit in the rightmost position.

The check digit is calculated as follows:
1. Beginning on the right, with the digit that immediately precedes the check digit and moving toward the left, double every other digit. After doubling each selected digit, if the result is ten or greater, add the two digits together to arrive at a single-digit result.

 4012 8888 8888 1881 02 88 88 81 8022 7878 7878 2871

2. Each individual resulting digit, plus those bypassed, above is then added together.
 8022 7878 7878 2871 8+0+2+2+7+8+7+8+7+8+7+8+2+8+7+1 = 90
3. This sum is then subtracted from the lowest multiple of ten that is equal to or greater than the sum, and the single-digit result is the check digit.
 90 ÷ 10 = 9 90 Mod 10 = 0
 Enter a Valid Credit Card Number:
 Example: 15-Digit Account Number 3714 4963 5398 431 15: 14: 13: 12: 11: 10: 9: 8: 7: 6: 5: 4: 3: 2: 1: 0: 1 x 1 = 1 3 x 2 = 6 : 6 4 x 1 = 4 8 x 2 = 16 : 7 9 x 1 = 9 3 x 2 = 6 : 6 5 x 1 = 5 3 x 2 = 6 : 6 6 x 1 = 6 9 x 2 = 18 : 9 4 x 1 = 4 4 x 2 = 8 : 8 1 x 1 = 1 7 x 2 = 14 : 5 3 x 1 = 3 0 x 2 = 0 : 0 Sum: 80

Note: Many programs written only to verify such numbers begin with the check digit itself (weighted as 1) and simply assure that the result is a multiple of ten.