Brian Dunning's FileMaker Custom Functions

CheckIBAN ( IBAN )

check if given iban number is correct ( EU version )

  Average rating: 4.2 (33 votes) Log in to vote

Michael Bijnens   Michael Bijnens
freelance developer

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  Sample input:
CheckIBAN ( BE55000311190144 )
  Sample output:

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

Michael Bijnens - Junior FileMaker Analyst / Programmer

You can use this custom function to check if the given IBAN number is correct.
Create a calculated field ( e.g. flag_correct_IBAN ) in the same table as your IBAN field. (output of the calculation-field has to be TEXT ).


1) given IBAN : BE55000311190144
2) first 4 to the end : "000311190144" & "BE55"
3) convert each letter ( B & E ) to digits. ( A = 10 ; B = 11 ; ... Z = 35 )
4) converted : 11 & 14
5) stich it : "000311190144" & "11" & "14" & "55" = 000311190144111455
6) Mod ( IBAN ; 97 )
7) if result = 1 than its a correct IBAN number



wwdto   wwdto, Munich
Feb 17, 2014
CAUTION! this Version this custom function does not work correct, it returns other values than 1 for correct IBANS from DE AT; CH and IT. Thats what I have tested.
Michael   Michael, Belgium
Feb 17, 2014
Thats correct. The Custom Function is only tested for Belgian IBANS.
I haven't tested IBANS from abroad.

I will repost is it if I have time to find out how it works.

Greets Michael.
wwdto   wwdto, munich
Feb 17, 2014
Thanks for your response. You can rename your function to CheckIBAN_BE(IBAN) and nobody will expect another result.

If you touch it: Would be fine if also length for the chosen country is checked. So this function could be used for input-testing.

Ideal would be an Error-code as return value, e.g 1=ok, 2=length-error, 4=special Charakter in IBAN etc. We already had this: a IBAN was copied from another application into a FileMaker field (WIN), nothing to see, nothing worked, hard to find out.

Greetings Wolfgang
Michael   Michael, Belgium
Feb 17, 2014
Changed it to an EU version.

check_length ( check if the length of IBAN number is correct with the given country code ).

1 = correct iban ;
missing country code = if country code is missing it won't be able to check length ) ;
incorrect iban = the length is correct but the number is incorrect ;
length error = the length of IBAN is incorrect.

Grtz Michael
Arjen van der Ree   Arjen van der Ree, Amsterdam
Apr 9, 2014
Hi Michael,

your solution does not seem to handle dutch bans correctly, probably because those have 2 sets of letterblocks (e.g. NL75INGB0005151989 ).

Perhaps something you could look into?

With Regards,

Arjen van der Ree
Amsterdam, the Neighbors
claude pirlot   claude pirlot, Brussels
Nov 1, 2015
Thank you very much for the IBAN Checker
Have a great week
Christoph Kaufmann   Christoph Kaufmann,
Apr 13, 2016
The functions says IBAN INCORRECT when it actually is correct:
IT06 A081 4034 5200 0000 9060 829

Reason: the function assumes there are but two letters in any IBAN (Position 1 and Position 2). Any IBAN with more than these two letters are wrongly valuated as false.

You have to convert every letter into a number. There's an example in

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