UK Bank Modulus Check Library

v1.13.0 2021-12-09 13:03 UTC


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This PHP library allows you to check the validity of UK bank account information. To perform this task it uses publicly available information and the specifications published by VocaLink.

You must be aware that this library cannot tell you that the account number and sort code associate to an active account, it only tells you that they could be assigned to an account. Neither does it cover all sort codes, some of which are outside the specification and you should assume those details are valid unless otherwise known.



This library provides a simple class to perform bank account validation and normalisation, through the BankModulus class.

By default the BankModulus class will use the current modulus specification issued by VocaLink, the default specification factory will pick the correct specification based on the date.

  • normalize(string &$sortCode, string &$accountNumber)

    This performs normalisation of sort code and account numbers according to rules issued by some banks. As an example 6 digit account numbers get padded with two zeros.

    The result of normalisation is assigned back to the input parameters.

  • check(string $sortCode, string $accountNumber) : boolean

    This is the primary method to ascertain if the details supplied are invalid, it returns false if the sort code and account number are invalid otherwise it will return true. If the details provided are syntactically valid but fall outside the specification then this method considers them valid.

  • lookup(string $sortCode, string $accountNumber) : Result

    Use this method to fetch more in depth information on the sort code and account number. See documentation on the Result class for more information.

  • __construct(SpecFactoryInterface $specFactory, NormalizerInterface $normalizer)

    You can change which specification factory and normalizer is used at the time of construction, otherwise defaults will be used.

  • Example:

    use Cs278\BankModulus\BankModulus;
    $modulus = new BankModulus();
    $modulus->check('08-16-32', '12481632');
    $sortCode = '12-24-48';
    $accountNumber = '123456';
    $modulus->normalize($sortCode, $accountNumber);
    var_dump($sortCode, $accountNumber);
    // string(6) "122448"
    // string(8) "00123456"

Result class

The Result class provides detailed information on the validation and normalisation results.

  • getSortCode() : SortCode

    Returns a SortCode object representing the normalised sort code.

  • getAccountNumber() : string

    Returns a string of the normalised account number.

  • isValidated() : boolean

    Returns a boolean which is true iff the sort code and account number could be validated using the specification.

  • isValid($assume = true) : boolean

    Returns a boolean representing the result of the modulus validation, if the sort code and account number could not be validated the value of the $assume argument is returned.

Specification Factory

The default specification factory (Spec\DefaultSpecFactory) picks the most appropriate specification for the current time.

If you need to test the validity of a sort code and account number at a particular point in time, you can use the withDate(\DateTimeInterface|string $date): self method to overload the currently used time reference. If you supply an object to this method it will convert it to the date in Europe/London, string date is used verbatim.


This library will throw exceptions implementing Exception\Exception if something unexpected occurs.

  • Exception\AccountNumberInvalidException

    The supplied account number was not a string of 8 numerical digits.

  • Exception\CannotValidateException

    This is thrown by an instance of Spec\SpecInterface when it cannot determine if the details are correct because they fall outside the specification.

  • Exception\SortCodeInvalidException

    The supplied sort code was not a string of 6 numerical digits.

Modulus Algorithms

Currently this library implements 3 similar algorithms to perform modulus calculations, these are defined in the VocaLink specification.

  • Standard Modulus (Mod10/Mod11)

    Multiplication of each digit in sort code and account number with a corresponding weight value, the results are summed and then divided by 10 or 11 depending on the algorithm being used. A remainder of 0 means the input was valid.

  • Double Alternate (DblAl)

    Each digit of the sort code and account number is multiplied by the corresponding weight value, each result is then split into digits and summed (e.g. 24 becomes 2+4). Then the results are summed and divided by 10, again a remainder of 0 is indicative of success.