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:
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
[8]0[2]2 [16]8[16]8 [16]8[16]8 [2]8[16]1
8022 7878 7878 2871
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
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.