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Luhn ( number )

The Luhn Mod-10 algorithm used to validate credit card numbers

  Average rating: 3.8 (43 votes) Log in to vote

Geoff Wells DataIsland Software LLC http://www.dataisland.com

  Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

/* The Luhn Mod-10 algorithm is used to validate ( check for input errors ) of many credit cards and Canadian Social Security numbers. This is a custom function implementation of the method used by Brian dunning in his Card Validator example. The functions LuhnDoubleEven and LuhnProduct are required for it to operate and must me defined prior to defining this function. */ Let( [ justNumbers = Filter( number ; "0123456789" ) ; // remove any non-numeric characters oddOrEvenLength = Mod(Length(justNumbers) ; 2) ; // odd length numbers return 1, even length numbers return 0 makeEven = Case(OddorEvenLength = 1; "0" ; "") & justNumbers ; // adds 0 to the front of any odd length number to make it even doubleEven = LuhnDoubleEven ( makeEven ) ; // doubles every 2nd number product = LuhnProduct ( doubleEven ) ; // Adds all the numbers together valid = Case( Mod( product ; 10 ) = 0 ; 1 ; 0 ) // The number is valid if it is exactly divisible by 10 ] ; // close let variable definition valid // return result ) // close let Click to copy

The Luhn Mod-10 algorithm is used to validate ( check for input errors ) of many credit cards and Canadian Social Security numbers.

 

Comments

		Chris, NY Jul 15, 2009
This function is perfect. Thank you for your good comments.

		Dave C., Vancouver, Canada May 1, 2015
Works great (once I realized I needed to put in 'number' as a parameter for Luhn, 'doubleEven' for LuhnProduct; and 'makeEven' for LuhnDoubleEven).

		Will Loving, Dedication Technologies, Inc. Mar 18, 2019
I'm testing this with a (fake but valid) China UnionPay 19-digit card number: 6264077021846833676 The card generator I'm using says it passes Luhn but it fails your Luhn Custom Function test along with any credit card validator based on it... Does the calculation require revision to handle 19-digit numbers?

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