RegEx for matching UK Postcodes

Question

I m after a regex that will validate a full complex UK postcode only within an input string  All of the uncommon postcode forms must be covered as well as the usual  For instance   Matches   CW3 9SS SE5 0EG SE50EG se5 0eg WC2H 7LT   No Match   aWC2H 7LT WC2H 7LTa WC2H   How do I solve this problem

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Some of the regexs above are a little restrictive. Note the genuine postcode: "W1K 7AA" would fail given the rule "Position 3 - AEHMNPRTVXY only used" above as "K" would be disallowed.

the regex:

^(GIR 0AA|[A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKPS-UW])[0-9][ABD-HJLNP-UW-Z]{2})$

Seems a little more accurate, see the Wikipedia article entitled 'Postcodes in the United Kingdom'.

Note that this regex requires uppercase only characters.

The bigger question is whether you are restricting user input to allow only postcodes that actually exist or whether you are simply trying to stop users entering complete rubbish into the form fields. Correctly matching every possible postcode, and future proofing it, is a harder puzzle, and probably not worth it unless you are HMRC.

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Here s a regex based on the format specified in the documents which are linked to marcj s answer      A-Z  1 2  0-9  0-9A-Z     0-9  A-Z  2      The only difference between that and the specs is that the last 2 characters cannot be in  CIKMOV  according to the specs   Edit  Here s another version which does test for the trailing character limitations      A-Z  1 2  0-9  0-9A-Z     0-9  A-BD-HJLNP-UW-Z  2

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Through empirical testing and observation  as well as confirming with https   en wikipedia org wiki Postcodes in the United Kingdom Validation  here is my version of a Python regex that correctly parses and validates a UK postcode   UK POSTCODE REGEX   r   P lt postcode area gt  A-Z  1 2    P lt district gt     0-9  1 2       0-9  A-Z     P lt sector gt  0-9    P lt postcode gt  A-Z  2     This regex is simple and has capture groups  It does not include all of the validations of legal UK postcodes  but only takes into account the letter vs number positions   Here is how I would use it in code    dataclass class UKPostcode      postcode area  str     district  str     sector  int     postcode  str        https   en wikipedia org wiki Postcodes in the United Kingdom Validation       Original author of this regex   jontsai       NOTE TO FUTURE DEVELOPER        Verified through empirical testing and observation  as well as confirming with the Wiki article       If this regex fails to capture all valid UK postcodes  then I apologize  for I am only human      UK POSTCODE REGEX   r   P lt postcode area gt  A-Z  1 2    P lt district gt     0-9  1 2       0-9  A-Z     P lt sector gt  0-9    P lt postcode gt  A-Z  2          classmethod     def from postcode cls  postcode              Parses a string into a UKPostcode          Returns a UKPostcode or None                     m   re match cls UK POSTCODE REGEX  postcode replace                    if m              uk postcode   UKPostcode                  postcode area m group  postcode area                    district m group  district                    sector m group  sector                    postcode m group  postcode                         else              uk postcode   None          return uk postcode   def parse uk postcode postcode          Wrapper for UKPostcode from postcode             uk postcode   UKPostcode from postcode postcode      return uk postcode   Here are unit tests    pytest mark parametrize       postcode  expected               https   en wikipedia org wiki Postcodes in the United Kingdom Validation                        EC1A1BB               UKPostcode                  postcode area  EC                   district  1A                   sector  1                   postcode  BB                                                   W1A0AX               UKPostcode                  postcode area  W                   district  1A                   sector  0                   postcode  AX                                                   M11AE               UKPostcode                  postcode area  M                   district  1                   sector  1                   postcode  AE                                                   B338TH               UKPostcode                  postcode area  B                   district  33                   sector  8                   postcode  TH                                                  CR26XH               UKPostcode                  postcode area  CR                   district  2                   sector  6                   postcode  XH                                                  DN551PT               UKPostcode                  postcode area  DN                   district  55                   sector  1                   postcode  PT                                  def test parse uk postcode postcode  expected       uk postcode   parse uk postcode postcode      assert uk postcode    expected

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An old post but still pretty high in google results so thought I d update   This Oct 14 doc defines the UK postcode regular expression as      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2        AZ  a-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2      from   https   www gov uk government uploads system uploads attachment data file 359448 4  Bulk Data Transfer - additional validation valid pdf  The document also explains the logic behind it   However  it has an error  bolded  and also allows lower case  which although legal is not usual  so amended version     GIR 0AA      A-Z  0-9  1 2      A-Z  A-HJ-Y  0-9  1 2      A-Z  0-9  A-Z     A-Z  A-HJ-Y  0-9   A-Z       0-9  A-Z  2      This works with new London postcodes  e g  W1D 5LH  that previous versions did not

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Most of the answers here didn t work for all the postcodes I have in my database  I finally found one that validates with all  using the new regex provided by the government   https   www gov uk government uploads system uploads attachment data file 413338 Bulk Data Transfer - additional validation valid from March 2015 pdf  It isn t in any of the previous answers so I post it here in case they take the link down      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      A-Za-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2      UPDATE  Updated regex as pointed by Jamie Bull  Not sure if it was my error copying or it was an error in the government s regex  the link is down now      UPDATE  As ctwheels found  this regex works with the javascript regex flavor  See his comment for one that works with the pcre  php  flavor

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Have a look at the python code on this page  http   www brunningonline net simon blog archives 001292 html  I ve got some postcode parsing to do  The requirement is pretty simple  I have to parse a postcode into an outcode and  optional  incode  The good new is that I don t have to perform any validation - I just have to chop up what I ve been provided with in a vaguely intelligent manner  I can t assume much about my import in terms of formatting  i e  case and embedded spaces  But this isn t the bad news  the bad news is that I have to do it all in RPG   -  Nevertheless  I threw a little Python function together to clarify my thinking   I ve used it to process postcodes for me

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I use the following regex that I have tested against all valid UK postcodes  It is based on the recommended rules  but condensed as much as reasonable and does not make use of any special language specific regex rules     A-PR-UWYZ   A-HK-Y  0-9   0-9   ABEHMNPRV-Y     0-9   0-9   A-HJKPSTUW       0-9  ABD-HJLNP-UW-Z  2     It assumes that the postcode has been converted to uppercase and has not leading or trailing characters  but will accept an optional space between the outcode and incode   The special  GIR0 0AA  postcode is excluded and will not validate as it s not in the official Post Office list of postcodes and as far as I m aware will not be used as registered address  Adding it should be trivial as a special case if required

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Postcodes are subject to change  and the only true way of validating a postcode is to have the complete list of postcodes and see if it s there   But regular expressions are useful because they    are easy to use and implement are short are quick to run are quite easy to maintain  compared to a full list of postcodes  still catch most input errors   But regular expressions tend to be difficult to maintain  especially for someone who didn t come up with it in the first place   So it must be    as easy to understand as possible relatively future proof   That means that most of the regular expressions in this answer aren t good enough   E g  I can see that  A-PR-UWYZ  A-HK-Y  0-9  ABEHMNPRV-Y  is going to match a postcode area of the form AA1A     but it s going to be a pain in the neck if and when a new postcode area gets added  because it s difficult to understand which postcode areas it matches   I also want my regular expression to match the first and second half of the postcode as parenthesised matches   So I ve come up with this    GIR    s 0AA      BEGLMNSW   A-Z  2   0-9     0-9     lt  N1 E1 SE1 SW1 W1 NW1 EC 0-9  WC 0-9   A-HJ-NP-Z     s   0-9  ABD-HJLNP-UW-Z  2     In PCRE format it can be written as follows          GIR    s 0AA    Match the special postcode  GIR 0AA                       BEGLMNSW      There are 8 single-letter postcode areas        A-Z  2        All other postcode areas have two letters              0-9    There is always at least one number after the postcode area                0-9    And an optional extra number                 Only certain postcode areas can have an extra letter after the number          lt  N1 E1 SE1 SW1 W1 NW1 EC 0-9  WC 0-9          A-HJ-NP-Z    Possible letters here may change  but  IO  will never be used                   s      0-9  ABD-HJLNP-UW-Z  2     The last two letters cannot be  CIKMOV    x   For me this is the right balance between validating as much as possible  while at the same time future-proofing and allowing for easy maintenance

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I needed a version that would work in SAS with the PRXMATCH and related functions  so I came up with this     A-PR-UWYZ    A-HK-Y   d d     d A-HJKPSTUW     A-HK-Y  d ABEHMNPRV-Y    s  d ABD-HJLNP-UW-Z  2     Test cases and notes       Notes The letters QVX are not used in the 1st position  The letters IJZ are not used in the second position  The only letters to appear in the third position are ABCDEFGHJKPSTUW when the structure starts with A9A  The only letters to appear in the fourth position are ABEHMNPRVWXY when the structure starts with AA9A  The final two letters do not use the letters CIKMOV  so as not to resemble digits or each other when hand-written             Bits and pieces     1st position  any            A-PR-UWYZ               2nd position  if letter      A-HK-Y      3rd position  A1A format     A-HJKPSTUW      4th position  AA1A format    ABEHMNPRV-Y      Last 2 positions             ABD-HJLNP-UW-Z           data example  infile cards truncover  input valid 1  postcode  amp  10  Notes  amp  100   flag   prxmatch     A-PR-UWYZ    A-HK-Y   d d     d A-HJKPSTUW     A-HK-Y  d ABEHMNPRV-Y    s  d ABD-HJLNP-UW-Z  2     strip postcode    cards  1  EC1A 1BB  Special case 1 1  W1A 0AX   Special case 2 1  M1 1AE    Standard format 1  B33 8TH   Standard format 1  CR2 6XH   Standard format 1  DN55 1PT  Standard format 0  QN55 1PT  Bad letter in 1st position 0  DI55 1PT  Bad letter in 2nd position 0  W1Z 0AX   Bad letter in 3rd position 0  EC1Z 1BB  Bad letter in 4th position 0  DN55 1CT  Bad letter in 2nd group 0  A11A 1AA  Invalid digits in 1st group 0  AA11A 1AA  1st group too long 0  AA11 1AAA  2nd group too long 0  AA11 1AAA  2nd group too long 0  AAA 1AA   No digit in 1st group 0  AA 1AA    No digit in 1st group 0  A 1AA     No digit in 1st group 0  1A 1AA    Missing letter in 1st group 0  1 1AA     Missing letter in 1st group 0  11 1AA    Missing letter in 1st group 0  AA1 1A    Missing letter in 2nd group 0  AA1 1     Missing letter in 2nd group   run

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here s how we have been dealing with the UK postcode issue      A-Za-z  1 2  0-9  1 2  A-Za-z         0-9  1  A-Za-z  2      Explanation    expect 1 or 2 a-z chars  upper or lower fine expect 1 or 2 numbers expect 0 or 1 a-z char  upper or lower fine optional space allowed expect 1 number expect 2 a-z  upper or lower fine   This gets most formats  we then use the db to validate whether the postcode is actually real  this data is driven by openpoint https   www ordnancesurvey co uk opendatadownload products html  hope this helps

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We were given a spec   UK postcodes must be in one of the following forms  with one exception  see below           A9 9AA         A99 9AA        AA9 9AA        AA99 9AA        A9A 9AA        AA9A 9AA where A represents an alphabetic character and 9 represents a numeric character  Additional rules apply to alphabetic characters  as follows         The character in position 1 may not be Q  V or X        The character in position 2 may not be I  J or Z        The character in position 3 may not be I  L  M  N  O  P  Q  R  V  X  Y or Z        The character in position 4 may not be C  D  F  G  I  J  K  L  O  Q  S  T  U or Z        The characters in the rightmost two positions may not be C  I  K  M  O or V The one exception that does not follow these general rules is the postcode  GIR 0AA   which is a special valid postcode   We came up with this        A-PR-UWYZ  A-HK-Y0-9     A-HJKS-UW0-9  ABEHMNPRV-Y0-9     s  0-9  ABD-HJLNP-UW-Z  2  GIR s 0AA   i   But note - this allows any number of spaces in between groups

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I ve been looking for a UK postcode regex for the last day or so and stumbled on this thread  I worked my way through most of the suggestions above and none of them worked for me so I came up with my own regex which  as far as I know  captures all valid UK postcodes as of Jan  13  according to the latest literature from the Royal Mail    The regex and some simple postcode checking PHP code is posted below  NOTE - It allows for lower or uppercase postcodes and the GIR 0AA anomaly but to deal with the  more than likely  presence of a space in the middle of an entered postcode it also makes use of a simple str replace to remove the space before testing against the regex  Any discrepancies beyond that and the Royal Mail themselves don t even mention them in their literature  see http   www royalmail com sites default files docs pdf programmers guide edition 7 v5 pdf and start reading from page 17    Note  In the Royal Mail s own literature  link above  there is a slight ambiguity surrounding the 3rd and 4th positions and the exceptions in place if these characters are letters  I contacted Royal Mail directly to clear it up and in their own words  A letter in the 4th position of the Outward Code with the format AANA NAA has no exceptions and the 3rd position exceptions apply only to the last letter of the Outward Code with the format ANA NAA   Straight from the horse s mouth    lt  php       postcoderegex        g  i  r  0  a  a         a-pr-uwyz  1   0   1-9  d      a-pr-uwyz  1  a-hk-y  1   0   1-9  d      a-pr-uwyz  1  1-9  a-hjkps-uw  1     a-pr-uwyz  1  a-hk-y  1  1-9  a-z  1     d abd-hjlnp-uw-z  2      i         postcode2check   str replace         postcode2check        if  preg match  postcoderegex   postcode2check              echo   postcode2check is a valid postcode lt br gt           else            echo   postcode2check is not a valid postcode lt br gt              gt    I hope it helps anyone else who comes across this thread looking for a solution

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I have the regex for UK Postcode validation   This is working for all type of Postcode either inner or outer       A-PR-UWYZ  0-9     A-PR-UWYZ  0-9  0-9     A-PR-UWYZ  A-HK-Y  0-9     A-PR-UWYZ  A-HK-Y  0-9  0-9     A-PR-UWYZ  0-9  A-HJKSTUW     A-PR-UWYZ  A-HK-Y  0-9  ABEHMNPRVWXY           GIR      0AA        A-PR-UWYZ  0-9        0-9  ABD-HJLNPQ-UW-Z  0 2         A-PR-UWYZ  0-9  0-9        0-9  ABD-HJLNPQ-UW-Z  0 2         A-PR-UWYZ  A-HK-Y0-9  0-9        0-9  ABD-HJLNPQ-UW-Z  0 2         A-PR-UWYZ  A-HK-Y0-9  0-9  0-9        0-9  ABD-HJLNPQ-UW-Z  0 2         A-PR-UWYZ  0-9  A-HJKS-UW0-9        0-9  ABD-HJLNPQ-UW-Z  0 2         A-PR-UWYZ  A-HK-Y0-9  0-9  ABEHMNPRVWXY0-9        0-9  ABD-HJLNPQ-UW-Z  0 2       This is working for all type of format   Example      AB10-------------------- ONLY OUTER POSTCODE      A1 1AA------------------ COMBINATION OF  OUTER AND INNER  POSTCODE      WC2A-------------------- OUTER

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According to this Wikipedia table    This pattern cover all the cases       A-Za-z  d   d A-Za-z  2       A-Za-z  A-Za-z d  d   d A-Za-z  2       A-Za-z  2  d 2    d A-Za-z  2       A-Za-z  d A-Za-z    d A-Za-z  2       A-Za-z  2  d A-Za-z    d A-Za-z  2     When using it on Android Java use   d

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Below method will check the post code and provide complete info  const valid postcode   postcode   gt        try           postcode   postcode replace   s g               const fromat   postcode              toUpperCase                match     A-Z  1 2  d 1 2  A-Z    s   d A-Z  2               const finalValue      fromat 1     fromat 2             const regex       Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z      0-9  A-Za-z  2    i          return               isValid  regex test postcode               formatedPostCode  finalValue              error  false              info   It is a valid postcode                   catch  error            return   error  true   info   Invalid post code has been entered                valid postcode  GU348RR   result   gt   isValid  true  formatedPostCode   GU34 8RR   error  false  info   It is a valid postcode     valid postcode  sdasd4746asd   result   gt   error  true  info   Invalid post code has been entered      valid postcode  787898523   result   gt   error  true  info   Invalid post code has been entered

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What i have found in nearly all the variations and the regex from the bulk transfer pdf and what is on wikipedia site is this  specifically for the wikipedia regex is  there needs to be a   after the first   vertical bar   I figured this out by testing for AA9A 9AA  because otherwise the format check for A9A 9AA will validate it  For Example checking for EC1D 1BB which should be invalid comes back valid because C1D 1BB is a valid format   Here is what I ve come up with for a good regex      G  I  R  0 A  2        A-Z- QVX   0-9  1 2     A-Z- QVX   A-HK-Y  0-9  1 2     A-Z- QVX   0-9  ABCDEFGHJKPSTUW     A-Z- QVX   A-HK-Y  0-9  ABEHMNPRVWXY     0-9  A-Z- CIKMOV   2

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First half of postcode Valid formats     A-Z  A-Z  0-9  A-Z    A-Z  A-Z  0-9  0-9    A-Z  0-9  0-9    A-Z  A-Z  0-9    A-Z  A-Z  A-Z    A-Z  0-9  A-Z    A-Z  0-9      Exceptions Position 1 - QVX not used Position 2 - IJZ not used except in GIR 0AA Position 3 - AEHMNPRTVXY only used Position 4 - ABEHMNPRVWXY     Second half of postcode      0-9  A-Z  A-Z       Exceptions Position 2 3 - CIKMOV not used  Remember not all possible codes are used  so this list is a necessary but not sufficent condition for a valid code  It might be easier to just match against a list of all valid codes

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To check a postcode is in a valid format as per the Royal Mail s programmer s guide              ----------------------------outward code------------------------------   ------inward code-----   special        a1        a2    AAN  AANA      AANN      AN    ANN    ANA  a3         N         AA   GIR 0AA  A-PR-UWYZ   A-HK-Y   0-9  A-Z    1-9  0-9    1-9   0-9   A-HJKPSTUW      0-9  ABD-HJLNP-UW-Z  2      All postcodes on doogal co uk match  except for those no longer in use   Adding a   after the space and using case-insensitive match to answer this question    se50eg  match    GIR 0AA  A-PR-UWYZ   A-HK-Y   0-9  A-Z    1-9  0-9    1-9   0-9   A-HJKPSTUW       0-9  ABD-HJLNP-UW-Z  2    ig   Array    se50eg

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I stole this from an XML document and it seems to cover all cases without the hard coded GIRO    r  A-Z  1 2  0-9R  0-9A-Z    0-9  A-Z  2  i    Ruby syntax with ignore case

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I recently posted an answer to this question on UK postcodes for the R language  I discovered that the UK Government s regex pattern is incorrect and fails to properly validate some postcodes  Unfortunately  many of the answers here are based on this incorrect pattern   I ll outline some of these issues below and provide a revised regular expression that actually works     Note  My answer  and regular expressions in general     Only validates postcode formats  Does not ensure that a postcode legitimately exists    For this  use an appropriate API  See Ben s answer for more info       If you don t care about the bad regex and just want to skip to the answer  scroll down to the Answer section   The Bad Regex  The regular expressions in this section should not be used   This is the failing regex that the UK government has provided developers  not sure how long this link will be up  but you can see it in their Bulk Data Transfer documentation       Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z      0-9  A-Za-z  2      Problems  Problem 1 - Copy Paste  See regex in use here   As many developers likely do  they copy paste code  especially regular expressions  and paste them expecting them to work  While this is great in theory  it fails in this particular case because copy pasting from this document actually changes one of the characters  a space  into a newline character as shown below      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2      The first thing most developers will do is just erase the newline without thinking twice  Now the regex won t match postcodes with spaces in them  other than the GIR 0AA postcode    To fix this issue  the newline character should be replaced with the space character      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2                                                                                                                                                             Problem 2 - Boundaries  See regex in use here      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2                                                                                                                                                                               The postcode regex improperly anchors the regex  Anyone using this regex to validate postcodes might be surprised if a value like fooA11 1AA gets through  That s because they ve anchored the start of the first option and the end of the second option  independently of one another   as pointed out in the regex above   What this means is that    asserts position at start of the line  only works on the first option   Gg  Ii  Rr  0 Aa  2    so the second option will validate any strings that end in a postcode  regardless of what comes before    Similarly  the first option isn t anchored to the end of the line    so GIR 0AAfoo is also accepted      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z      0-9  A-Za-z  2      To fix this issue  both options should be wrapped in another group  or non-capturing group  and the anchors placed around that        Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2                                                                                                                                                                                  Problem 3 - Improper Character Set  See regex in use here      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2                                                                                                The regex is missing a - here to indicate a range of characters  As it stands  if a postcode is in the format ANA NAA  where A represents a letter and N represents a number   and it begins with anything other than A or Z  it will fail   That means it will match A1A 1AA and Z1A 1AA  but not B1A 1AA   To fix this issue  the character - should be placed between the A and Z in the respective character set      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      A-Za-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2                                                                                                Problem 4 - Wrong Optional Character Set  See regex in use here      Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0-9  A-Za-z  2                                                                                                                                                I swear they didn t even test this thing before publicizing it on the web  They made the wrong character set optional  They made  0-9  option in the fourth sub-option of option 2  group 9   This allows the regex to match incorrectly formatted postcodes like AAA 1AA   To fix this issue  make the next character class optional instead  and subsequently make the set  0-9  match exactly once       Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      AZa-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9  A-Za-z        0-9  A-Za-z  2                                                                                                                                                        Problem 5 - Performance  Performance on this regex is extremely poor  First off  they placed the least likely pattern option to match GIR 0AA at the beginning  How many users will likely have this postcode versus any other postcode  probably never  This means every time the regex is used  it must exhaust this option first before proceeding to the next option  To see how performance is impacted check the number of steps the original regex took  35  against the same regex after having flipped the options  22    The second issue with performance is due to the way the entire regex is structured  There s no point backtracking over each option if one fails  The way the current regex is structured can greatly be simplified  I provide a fix for this in the Answer section   Problem 6 - Spaces  See regex in use here  This may not be considered a problem  per se  but it does raise concern for most developers  The spaces in the regex are not optional  which means the users inputting their postcodes must place a space in the postcode  This is an easy fix by simply adding   after the spaces to render them optional  See the Answer section for a fix     Answer  1  Fixing the UK Government s Regex  Fixing all the issues outlined in the Problems section and simplifying the pattern yields the following  shorter  more concise pattern  We can also remove most of the groups since we re validating the postcode as a whole  not individual parts    See regex in use here     A-Za-z  A-Ha-hJ-Yj-y   0-9  A-Za-z0-9     0-9  A-Za-z  2   Gg  Ii  Rr   0 Aa  2      This can further be shortened by removing all of the ranges from one of the cases  upper or lower case  and using a case-insensitive flag  Note  Some languages don t have one  so use the longer one above  Each language implements the case-insensitivity flag differently   See regex in use here      A-Z  A-HJ-Y   0-9  A-Z0-9     0-9  A-Z  2  GIR  0A 2      Shorter again replacing  0-9  with  d  if your regex engine supports it    See regex in use here      A-Z  A-HJ-Y   d A-Z d     d A-Z  2  GIR  0A 2      2  Simplified Patterns  Without ensuring specific alphabetic characters  the following can be used  keep in mind the simplifications from 1  Fixing the UK Government s Regex have also been applied here    See regex in use here      A-Z  1 2  d A-Z d     d A-Z  2  GIR  0A 2      And even further if you don t care about the special case GIR 0AA     A-Z  1 2  d A-Z d     d A-Z  2     3  Complicated Patterns  I would not suggest over-verification of a postcode as new Areas  Districts and Sub-districts may appear at any point in time  What I will suggest potentially doing  is added support for edge-cases  Some special cases exist and are outlined in this Wikipedia article   Here are complex regexes that include the subsections of 3   3 1  3 2  3 3    In relation to the patterns in 1  Fixing the UK Government s Regex   See regex in use here      A-Z  A-HJ-Y   d A-Z d   ASCN STHL TDCU BBND  BFS IQQ PCRN TKCA    d A-Z  2  BFPO   d 1 4   KY d MSR VG AI   -   d 4   A-Z  2    d 2  GE  CX GIR  0A 2  SAN  TA1     And in relation to 2  Simplified Patterns   See regex in use here      A-Z  1 2  d A-Z d   ASCN STHL TDCU BBND  BFS IQQ PCRN TKCA    d A-Z  2  BFPO   d 1 4   KY d MSR VG AI   -   d 4   A-Z  2    d 2  GE  CX GIR  0A 2  SAN  TA1     3 1 British Overseas Territories  The Wikipedia article currently states  some formats slightly simplified     AI-1111  Anguila ASCN 1ZZ  Ascension Island STHL 1ZZ  Saint Helena TDCU 1ZZ  Tristan da Cunha BBND 1ZZ  British Indian Ocean Territory BIQQ 1ZZ  British Antarctic Territory FIQQ 1ZZ  Falkland Islands GX11 1ZZ  Gibraltar PCRN 1ZZ  Pitcairn Islands SIQQ 1ZZ  South Georgia and the South Sandwich Islands TKCA 1ZZ  Turks and Caicos Islands BFPO 11  Akrotiri and Dhekelia ZZ 11  amp  GE CX  Bermuda  according to this document  KY1-1111  Cayman Islands  according to this document  VG1111  British Virgin Islands  according to this document  MSR 1111  Montserrat  according to this document    An all-encompassing regex to match only the British Overseas Territories might look like this   See regex in use here      ASCN STHL TDCU BBND  BFS IQQ GX d 2  PCRN TKCA    d A-Z  2   KY d MSR VG AI   -   d 4   BFPO  A-Z  2     d 2  GE  CX     3 2 British Forces Post Office  Although they ve been recently changed it to better align with the British postcode system to BF   where   represents a number   they re considered optional alternative postcodes  These postcodes follow ed  the format of BFPO  followed by 1-4 digits   See regex in use here   BFPO   d 1 4     3 3 Santa   There s another special case with Santa  as mentioned in other answers   SAN TA1 is a valid postcode  A regex for this is very simply    SAN  TA1

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This is the regex Google serves on their i18napis appspot com domain   GIR    0AA   AB AL B BA BB BD BH BL BN BR BS BT BX CA CB CF CH CM CO CR CT CV CW DA DD DE DG DH DL DN DT DY E EC EH EN EX FK FY G GL GY GU HA HD HG HP HR HS HU HX IG IM IP IV JE KA KT KW KY L LA LD LE LL LN LS LU M ME MK ML N NE NG NN NP NR NW OL OX PA PE PH PL PO PR RG RH RM S SA SE SG SK SL SM SN SO SP SR SS ST SW SY TA TD TF TN TQ TR TS TW UB W WA WC WD WF WN WR WS WV YO ZE   d  dA-Z       d ABD-HJLN-UW-Z  2    BFPO     d 1 4

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The accepted answer reflects the rules given by Royal Mail  although there is a typo in the regex  This typo seems to have been in there on the gov uk site as well  as it is in the XML archive page    In the format A9A 9AA the rules allow a P character in the third position  whilst the regex disallows this  The correct regex would be    GIR 0AA      A-Z- QVX   0-9  0-9       A-Z- QVX   A-Z- IJZ   0-9  0-9       A-Z- QVX   0-9  A-HJKPSTUW     A-Z- QVX   A-Z- IJZ   0-9  ABEHMNPRVWXY       0-9  A-Z- CIKMOV   2      Shortening this results in the following regex  which uses Perl Ruby syntax     GIR 0AA    A-PR-UWYZ    0-9   0-9A-HJKPSTUW       A-HK-Y  0-9   0-9ABEHMNPRVWXY      s  0-9  ABD-HJLNP-UW-Z  2     It also includes an optional space between the first and second block

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A-PR-UWYZ0-9  A-HK-Y0-9  AEHMNPRTVXY0-9   ABEHMNPRVWXY0-9    1 2  0-9  ABD-HJLN-UW-Z  2  GIR 0AA        Regular expression to match valid UK   postcodes  In the UK postal system not   all letters are used in all positions    the same with vehicle registration   plates  and there are various rules to   govern this  This regex takes into   account those rules  Details of the   rules  First half of postcode Valid   formats  A-Z  A-Z  0-9  A-Z     A-Z  A-Z  0-9  0-9   A-Z  0-9  0-9     A-Z  A-Z  0-9   A-Z  A-Z  A-Z     A-Z  0-9  A-Z   A-Z  0-9  Exceptions   Position - First  Contraint - QVX not   used Position - Second  Contraint -   IJZ not used except in GIR 0AA   Position - Third  Constraint -   AEHMNPRTVXY only used Position -   Forth  Contraint - ABEHMNPRVWXY Second   half of postcode Valid formats    0-9  A-Z  A-Z  Exceptions Position -   Second and Third  Contraint - CIKMOV   not used   http   regexlib com REDetails aspx regexp id 260

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To add to this list a more practical regex that I use that allows the user to enter an empty string is          gG  iI  rR   0  0 aA  2       a-pr-uwyzA-PR-UWYZ  a-hk-yA-HK-Y   0-9  0-9       a-pr-uwyzA-PR-UWYZ  0-9  a-hjkstuwA-HJKSTUW     a-pr-uwyzA-PR-UWYZ  a-hk-yA-HK-Y  0-9  abehmnprv-yABEHMNPRV-Y      0 1  0-9  abd-hjlnp-uw-zABD-HJLNP-UW-Z  2       This regex allows capital and lower case letters with an optional space in between  From a software developers point of view this regex is useful for software where an address may be optional  For example if a user did not want to supply their address details

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I d recommend taking a look at the UK Government Data Standard for postcodes  link now dead  archive of XML  see Wikipedia for discussion   There is a brief description about the data and the attached xml schema provides a regular expression  It may not be exactly what you want but would be a good starting point  The RegEx differs from the XML slightly  as a P character in third position in format A9A 9AA is allowed by the definition given   The RegEx supplied by the UK Government was     Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      A-Za-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9  A-Za-z       s  0-9  A-Za-z  2     As pointed out on the Wikipedia discussion  this will allow some non-real postcodes  e g  those starting AA  ZY  and they do provide a more rigorous test that you could try

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I had a look into some of the answers above and I d recommend against using the pattern from  Dan s answer  c  Dec 15  10   since it incorrectly flags almost 0 4  of valid postcodes as invalid  while the others do not    Ordnance Survey provide service called Code Point Open which      contains a list of all the current postcode units in Great Britain   I ran each of the regexs above against the full list of postcodes  Jul 6  13  from this data using grep   cat CSV   csv         Strip leading quotes     sed -e  s     g          Strip trailing quote and everything after it     sed -e  s      g          Strip any spaces     sed -E -e  s     g          Find any lines that do not match the expression     grep --invert-match --perl-regexp   pattern    There are 1 686 202 postcodes total   The following are the numbers of valid postcodes that do not  match each  pattern       A-PR-UWYZ0-9  A-HK-Y0-9  AEHMNPRTVXY0-9   ABEHMNPRVWXY0-9   0-9  ABD-HJLN-UW-Z  2  GIR 0AA        gt  6016  0 36          GIR  0AA  A-PR-UWYZ   0-9  1 2    A-HK-Y  0-9   0-9ABEHMNPRV-Y      0-9  A-HJKPS-UW     0-9  ABD-HJLNP-UW-Z  2         gt  0       GIR    0AA   AB AL B BA BB BD BH BL BN BR BS BT BX CA CB CF CH CM CO CR CT CV CW DA DD DE DG DH DL DN DT DY E EC EH EN EX FK FY G GL GY GU HA HD HG HP HR HS HU HX IG IM IP IV JE KA KT KW KY L LA LD LE LL LN LS LU M ME MK ML N NE NG NN NP NR NW OL OX PA PE PH PL PO PR RG RH RM S SA SE SG SK SL SM SN SO SP SR SS ST SW SY TA TD TF TN TQ TR TS TW UB W WA WC WD WF WN WR WS WV YO ZE   d  dA-Z       d ABD-HJLN-UW-Z  2    BFPO     d 1 4        gt  0   Of course  these results only deal with valid postcodes that are incorrectly flagged as invalid  So              gt  0   I m saying nothing about which pattern is the best regarding filtering out invalid postcodes

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I wanted a simple regex  where it s fine to allow too much  but not to deny a valid postcode  I went with this  the input is a stripped trimmed string        a-z0-9  s   5 8   i   This allows the shortest possible postcodes like  L1 8JQ  as well as the longest ones like  OL14 5ET    Because it allows up to 8 characters  it will also allow incorrect 8 character postcodes if there is no space   OL145ETX   But again  this is a simplistic regex  for when that s good enough

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Basic rules     A-Z  1 2  0-9R  0-9A-Z    0-9  ABD-HJLNP-UW-Z  2     Postal codes in the U K   or postcodes  as they   re called  are composed of five to seven alphanumeric characters separated by a space  The rules covering which characters can appear at particular positions are rather complicated and fraught with exceptions  The regular expression just shown therefore sticks to the basic rules   Complete rules   If you need a regex that ticks all the boxes for the postcode rules at the expense of readability  here you go           A-PR-UWYZ  0-9  1 2   A-PR-UWYZ  A-HK-Y  0-9  1 2   A-PR-UWYZ  0-9  A-HJKSTUW   A-PR-UWYZ  A-HK-Y  0-9  ABEHMNPRV-Y    0-9  ABD-HJLNP-UW-Z  2  GIR 0AA     Source  https   www safaribooksonline com library view regular-expressions-cookbook 9781449327453 ch04s16 html  Tested against our customers database and seems perfectly accurate

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There is no such thing as a comprehensive UK postcode regular expression that is capable of validating a postcode  You can check that a postcode is in the correct format using a regular expression  not that it actually exists   Postcodes are arbitrarily complex and constantly changing  For instance  the outcode W1 does not  and may never  have every number between 1 and 99  for every postcode area   You can t expect what is there currently to be true forever  As an example  in 1990  the Post Office decided that Aberdeen was getting a bit crowded  They added a 0 to the end of AB1-5 making it AB10-50 and then created a number of postcodes in between these    Whenever a new street is build a new postcode is created  It s part of the process for obtaining permission to build  local authorities are obliged to keep this updated with the Post Office  not that they all do    Furthermore  as noted by a number of other users  there s the special postcodes such as Girobank  GIR 0AA  and the one for letters to Santa  SAN TA1 - you probably don t want to post anything there but it doesn t appear to be covered by any other answer   Then  there s the BFPO postcodes  which are now changing to a more standard format  Both formats are going to be valid  Lastly  there s the overseas territories source Wikipedia     ---------- ----------------------------------------------    Postcode                     Location                      ---------- ----------------------------------------------    AI-2640    Anguilla                                         ASCN 1ZZ   Ascension Island                                 STHL 1ZZ   Saint Helena                                     TDCU 1ZZ   Tristan da Cunha                                 BBND 1ZZ   British Indian Ocean Territory                   BIQQ 1ZZ   British Antarctic Territory                      FIQQ 1ZZ   Falkland Islands                                 GX11 1AA   Gibraltar                                        PCRN 1ZZ   Pitcairn Islands                                 SIQQ 1ZZ   South Georgia and the South Sandwich Islands     TKCA 1ZZ   Turks and Caicos Islands                        ---------- ----------------------------------------------   Next  you have to take into account that the UK  exported  its postcode system to many places in the world  Anything that validates a  UK  postcode will also validate the postcodes of a number of other countries   If you want to validate a UK postcode the safest way to do it is to use a look-up of current postcodes  There are a number of options    Ordnance Survey releases Code-Point Open under an open data licence  It ll be very slightly behind the times but it s free  This will  probably - I can t remember  not include Northern Irish data as the Ordnance Survey has no remit there  Mapping in Northern Ireland is conducted by the Ordnance Survey of Northern Ireland and they have their  separate  paid-for  Pointer product  You could use this and append the few that aren t covered fairly easily  Royal Mail releases the Postcode Address File  PAF   this includes BFPO which I m not sure Code-Point Open does  It s updated regularly but costs money  and they can be downright mean about it sometimes   PAF includes the full address rather than just postcodes and comes with its own Programmers Guide  The Open Data User Group  ODUG  is currently lobbying to have PAF released for free  here s a description of their position  Lastly  there s AddressBase  This is a collaboration between Ordnance Survey  Local Authorities  Royal Mail and a matching company to create a definitive directory of all information about all UK addresses  they ve been fairly successful as well   It s paid-for but if you re working with a Local Authority  government department  or government service it s free for them to use  There s a lot more information than just postcodes included

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This one allows empty spaces and tabs from both sides in case you don t want to fail validation and then trim it sever side     s    Gg  Ii  Rr  0 Aa  2       A-Za-z  0-9  1 2      A-Za-z  A-Ha-hJ-Yj-y  0-9  1 2      A-Za-z  0-9  A-Za-z     A-Za-z  A-Ha-hJ-Yj-y  0-9   A-Za-z       0 1  0-9  A-Za-z  2   s

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It looks like we re going to be using   GIR  0AA  A-PR-UWYZ   0-9  1 2    A-HK-Y  0-9   0-9ABEHMNPRV-Y      0-9  A-HJKPS-UW     0-9  ABD-HJLNP-UW-Z  2     which is a slightly modified version of that sugested by Minglis above   However  we re going to have to investigate exactly what the rules are  as the various solutions listed above appear to apply different rules as to which letters are allowed   After some research  we ve found some more information  Apparently a page on  govtalk gov uk  points you to a postcode specification govtalk-postcodes  This points to an XML schema at XML Schema which provides a  pseudo regex  statement of the postcode rules   We ve taken that and worked on it a little to give us the following expression      GIR  amp 0AA      A-PR-UWYZ  A-HK-Y   0-9  0-9       A-PR-UWYZ  0-9  A-HJKSTUW     A-PR-UWYZ  A-HK-Y  0-9  ABEHMNPRV-Y      amp  0-9  ABD-HJLNP-UW-Z  2       This makes spaces optional  but does limit you to one space  replace the   amp   with   0   for unlimited spaces   It assumes all text must be upper-case   If you want to allow lower case  with any number of spaces  use       gG  iI  rR   0  0 aA  2       a-pr-uwyzA-PR-UWYZ  a-hk-yA-HK-Y   0-9  0-9       a-pr-uwyzA-PR-UWYZ  0-9  a-hjkstuwA-HJKSTUW     a-pr-uwyzA-PR-UWYZ  a-hk-yA-HK-Y  0-9  abehmnprv-yABEHMNPRV-Y      0   0-9  abd-hjlnp-uw-zABD-HJLNP-UW-Z  2       This doesn t cover overseas territories and only enforces the format  NOT the existence of different areas  It is based on the following rules   Can accept the following formats       GIR 0AA    A9 9ZZ A99 9ZZ AB9 9ZZ AB99 9ZZ A9C 9ZZ AD9E 9ZZ   Where    9 can be any single digit number  A can be any letter except for Q  V or X  B can be any letter except for I  J or Z  C can be any letter except for I  L  M  N  O  P  Q  R  V  X  Y or Z  D can be any letter except for I  J or Z  E can be any of A  B  E  H  M  N  P  R  V  W  X or Y  Z can be any letter except for C  I  K  M  O or V    Best wishes  Colin

[regex] RegEx for matching UK Postcodes

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