How to check digits in credit card validation
Author: Hal Stiles | Section: Dev Resources | Date: 2005-06-25
This document outlines procedures and algorithms for Verifying the accuracy and validity of credit card numbers. Most credit card numbers are encoded with a "Check Digit". A check digit is a digit added to a number (either at the end or the beginning) that validates the authenticity of the number.
A simple algorithm is applied to the other digits of the number which yields the check digit. By running the algorithm, and comparing the check digit you get from the algorithm with the check digit encoded with the credit card number, you can verify that you have correctly read all of the digits and that they make a valid combination.
Possible uses for this information:
When a user has keyed in a credit card number (or scanned it) and you want to validate it before sending it our for debit authorization.
When issuing cards, say an affinity card, you might want to add a check digit using the MOD 10 method.
Prefix, Length, and Check Digit Criteria
Here is a table outlining the major credit cards that you might want to validate.
CARD TYPE
Prefix
Length
Check digit algorithm
MASTERCARD
51-55
16
mod 10
VISA
4
13, 16
mod 10
AMEX
34 37
15
mod 10
Diners Club / Carte wwdsb/p>
300-305 36 38
14
mod 10
Discover
6011
16
mod 10
enRoute
2014 2149
15
any
3
16
mod 10
2131 1800
15
mod 10
LUHN Formula (Mod 10) for Validation of Primary Account Number
The following steps are required to validate the primary account number:
Step 1: Double the value of alternate digits of the primary account number beginning with the second digit from the right (the first right--hand digit is the check digit.)
Step 2: Add the individual digits comprising the products obtained in Step 1 to each of the unaffected digits in the original number.
Step 3: The total obtained in Step 2 must be a number ending in zero (30, 40, 50, etc.) for the account number to be validated.
For example, to validate the primary account number 49927398716:
Step 1:
4 9 9 2 7 3 9 8 7 1 6
x2 x2 x2 x2 x2
------------------------------
18 4 6 16 2
Step 2:
4 +(1+8)+ 9 + (4) + 7 + (6) + 9 +(1+6) + 7 + (2) + 6
Step 3: Sum = 70 => Card number is validated
Note: Card is valid because the 70/10 yields no remainder.
Resources
The great folks at ICVERIFY are the original source of this data, I only formatted it in HTML.
If you are in the market, I wrote a set of FoxPro modules for Windows/Dos that interface nicely with ICVERIFY in a multi-user LAN setup. You just set up ICVERIFY on a single station, and all stations on the LAN can authorize credit cards with a single FOXBASE function call. Of course, you have to license ICVERIFY by the node, but it is very reasonable. I also wrote a couple of simple functions to perform pre-authorization, card screening, etc.
Here is a Microsoft Excel worksheet that will validate a number for you.
Because I get at least a letter a week regarding this routine, here are some additional helpful notes:
Make sure that you:
Have started with the rightmost digit (including the check digit) (figure odd and even based upon the rightmost digit being odd, regardless of the length of the Credit Card.) ALWAYS work right to left.
The check digit counts as digit #1 (assuming that the rightmost digit is the check digit) and is not doubled.
Double every second digit (starting with digit # 2 from the right).
Remember that when you double a number over 4, (6 for example) you don't add the result to your total, but rather the sum of the digits of the result (in the above example 6*2=12 so you would add 1+2 to your total (not 12).
Always include the Visa or M/C/ prefix.
Article was originally released on the Hal Stiles webpage server and in the Platon.SK content management system it is published with author and host administrator agreeement.
常用信用卡卡号规则
Issuer Identifier Card Number Length Diner's hxddp, 3095xx,36xxxx, 38xxxx 14 American Express 34xxxx, 37xxxx 15 VISA 4xxxxx 13, 16 MasterCard 51xxxx-55xxxx 16 JCB 3528xx-358xxx 16 Discover 6011xx 16 银联 622126-622925 16 信用卡号验证基本算法： 1、偶数位卡号奇数位上数字*2，奇数位卡号偶数位上数字*2。 2、大于10的位数减9。 3、全部数字加起来。 4、结果不是10的倍数的卡号非法。