These postcodes are structurally valid but fictional, for software testing and form design. This is not a Royal Mail postcode lookup: the Chesterfield districts are real, the full postcodes are not assigned to any address.
A random Chesterfield postcode generator combines a real Chesterfield postcode district with a generated inward code, producing a structurally valid postcode that is not assigned to any delivery point.
Every postcode on this page starts from a genuine Chesterfield postcode district. There are 5 of them, in the S postcode area, and they all belong to the CHESTERFIELD post town in Derbyshire. The three characters after the space are generated to the Royal Mail format rules, so a result validates in any form or database while belonging to no real property.
S42 7AA — district S42, sector S42 7, CHESTERFIELD, DerbyshireS42 5DX — district S42, sector S42 5, CHESTERFIELD, DerbyshireS43 5HD — district S43, sector S43 5, CHESTERFIELD, DerbyshireS41 9GH — district S41, sector S41 9, CHESTERFIELD, DerbyshireS41 2NY — district S41, sector S41 2, CHESTERFIELD, DerbyshireS43 1NJ — district S43, sector S43 1, CHESTERFIELD, DerbyshireThis page produces postcodes on their own. For complete Chesterfield addresses — building number, street, locality, post town, Derbyshire and postcode, laid out to Royal Mail conventions — use the random Chesterfield address generator.
A UK postcode splits into an outward code and an inward code. The outward code identifies the district; the inward code narrows it to a small group of properties. This generator keeps the first half real and generates the second, which is what makes the output safe to use and still valid.
Chesterfield sits in the S postcode area. Every district below is a real outward code assigned to the CHESTERFIELD post town.
| District | Locality | Structural range |
|---|---|---|
| S40 | — | S40 0AA – S40 9ZZ |
| S41 | — | S41 0AA – S41 9ZZ |
| S42 | — | S42 0AA – S42 9ZZ |
| S43 | — | S43 0AA – S43 9ZZ |
| S44 | — | S44 0AA – S44 9ZZ |
The structural range is what the postcode grammar permits for each district, not a list of codes Royal Mail has issued. Which sectors and units are actually allocated is Postcode Address File data, which is licensed and not held here — so a generated postcode inside the range may well be unallocated. For test data that is the point.
No locality names are listed for these districts. A locality is only recorded where a district is genuinely known by that neighbourhood name; where that was not established with confidence, the field is left empty rather than filled in with a guess.
A postcode carries more than a location. Reading one from Chesterfield tells you which country's addressing conventions apply, which ceremonial county the address sits in, and — if you need a matching telephone number — which dialling code area it falls in.
| Field | Value | Where it comes from |
|---|---|---|
| Post town | CHESTERFIELD | Royal Mail post town, written in capitals on the address |
| Postcode area | S | The leading letters of every district above |
| Ceremonial county | Derbyshire | ONS administrative geography |
| Country | England | One of the four countries of the United Kingdom |
| Region | East Midlands | ONS ITL1 statistical region |
| Dialling code | 01246 | Ofcom National Telephone Numbering Plan |
Royal Mail has not required a county line on addressed mail since 1996. CHESTERFIELD plus a correct postcode is sufficient; Derbyshire is included because plenty of address forms and legacy databases still expect a county.
What they are not for: sending post, verifying an identity, or implying that a property exists. If you need to know whether a Chesterfield address is deliverable, that is a licensed Royal Mail Postcode Address File lookup, and no generator can answer it.
The districts are real: all 5 of them are Royal Mail outward codes genuinely assigned to the CHESTERFIELD post town. The three characters after the space are generated, so the full postcode is almost certainly not allocated to any property. That combination is deliberate — the result resolves to Chesterfield in a district lookup and passes validation, but it is not a live delivery point and must never be used to send post.
5, in the S postcode area: S40, S41, S42, S43, S44. That is the count for the CHESTERFIELD post town as recorded in this site's registry; a post town does not follow council boundaries, so it may not match what a resident would call "Chesterfield".
S. The postcode area is the leading letter or letters of the outward code, so every Chesterfield postcode begins S — for example S40. The digits that follow identify the district within the area.
This page generates postcodes on their own and explains Chesterfield's district structure. The Chesterfield address generator produces complete postal addresses — building number, street, locality, post town, county and postcode — laid out to Royal Mail conventions. Use this page when you need postcodes to test a postcode field; use the address generator when you need whole addresses.
Yes, with no API key. Call GET /api/v1/postcodes/random?location=chesterfield&count=25 for JSON. Add &seed=1 to get the same set back on every request, which keeps snapshot tests stable. The response carries the outward code, inward code, area, district and sector for each postcode alongside the post town and county.
Structural validation, yes: the format, the length and the excluded letters are all respected, so a correctly written regex or a library check will accept them. A validator backed by licensed Postcode Address File data will reject most of them, correctly, because the full postcode is not an allocated delivery point. If your test suite needs addresses that pass a PAF lookup, no generator can supply them.
Postcodes are generated on demand and never stored. They are for software testing and development only, and must not be used to send post, to imply a real address, or for identity verification.