IBAN format · GB

United Kingdom IBAN format: 22 characters.

UK IBANs have 22 characters: the country code GB, two check digits and an 18-character BBAN, the national account number, laid out as 4!a6!n8!n.

United Kingdom IBAN structure

GB29NWBK60161331926819

Country code: GB
Check digits: 29
Bank code: NWBK
Branch code: 601613
Account: 31926819

Parts of a United Kingdom IBAN and their positions
Positions	Part	In the example
1–2	Country code	GB
3–4	Check digits	29
5–8	Bank code	NWBK
9–14	Branch code	601613
15–22	Account	31926819

The BBAN, segment by segment

The registry writes the BBAN in SWIFT notation: n is a digit, a an upper-case letter, c a letter or digit, and the ! means a fixed length. 4!a6!n8!n reads:

The United Kingdom BBAN format, segment by segment
Positions	Notation	Holds	Example
5–8	4!a	4 upper-case lettersBank code: the first four letters of the bank’s BIC	NWBK
9–14	6!n	6 digitsSort code	601613
15–22	8!n	8 digitsAccount number	31926819

United Kingdom IBAN example

GB29 NWBK 6016 1331 9268 19 is the sample the SWIFT IBAN Registry publishes for United Kingdom: a well-formed IBAN for showing the format, not a real account. Written electronically it has no spaces (GB29NWBK60161331926819); on paper it is printed in groups of four.

Its check digits, worked through with ISO 7064 mod 97-10:

Move the country code and check digits to the end
NWBK60161331926819GB29
Replace each letter with two digits (A = 10 … Z = 35)
N = 23, W = 32, B = 11, K = 20, G = 16
2332112060161331926819161129
Divide that number by 97 and keep the remainder
Remainder 1. A valid IBAN always leaves 1, so the check digits are right.
Where the check digits come from
Put 00 in their place (GB00…), repeat steps 1–3: remainder 69. The check digits are 98 − 69 = 29.

SEPA

United Kingdom is in the Single Euro Payments Area, so SEPA credit transfers and direct debits can reach GB IBANs; whether a given bank takes part is up to that bank.

Jersey, Guernsey and the Isle of Man use GB IBANs.

What the format can and can’t tell you

Valid means the structure and check digits are right — not that the account exists or can receive payments.
National check digits inside the BBAN (e.g. the French RIB key, or the Spanish, Belgian and Italian CIN digits) are not verified.
Bank and branch codes are read from their positions; they are not looked up in a bank directory.

Check GB IBANs from code or an AI agent

REST · GET · no key

curl -s 'https://payopskit.com/api/v1/iban/GB29NWBK60161331926819'

MCP · tools/call · validate_iban

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "validate_iban",
    "arguments": {
      "iban": "GB29NWBK60161331926819"
    }
  }
}

Response (JSON)

{
  "input": "GB29NWBK60161331926819",
  "iban": "GB29NWBK60161331926819",
  "print": "GB29 NWBK 6016 1331 9268 19",
  "valid": true,
  "country": {
    "code": "GB",
    "name": "United Kingdom",
    "sepa": true,
    "sepaNote": null
  },
  "checkDigits": "29",
  "expectedCheckDigits": "29",
  "length": {
    "actual": 22,
    "expected": 22
  },
  "bban": "NWBK60161331926819",
  "bbanFormat": "4!a6!n8!n",
  "bankCode": "NWBK",
  "branchCode": "601613",
  "parts": [
    {
      "label": "Country code",
      "value": "GB",
      "start": 0,
      "end": 2,
      "kind": "country"
    },
    {
      "label": "Check digits",
      "value": "29",
      "start": 2,
      "end": 4,
      "kind": "check"
    },
    {
      "label": "Bank code",
      "value": "NWBK",
      "start": 4,
      "end": 8,
      "kind": "bank"
    },
    {
      "label": "Branch code",
      "value": "601613",
      "start": 8,
      "end": 14,
      "kind": "branch"
    },
    {
      "label": "Account",
      "value": "31926819",
      "start": 14,
      "end": 22,
      "kind": "account"
    }
  ],
  "checks": {
    "characters": true,
    "country": true,
    "length": true,
    "bbanFormat": true,
    "checksum": true
  },
  "errors": [],
  "notes": [
    "Valid means the structure and check digits are right — not that the account exists or can receive payments.",
    "National check digits inside the BBAN (e.g. the French RIB key, or the Spanish, Belgian and Italian CIN digits) are not verified."
  ]
}

The MCP server is at /mcp (Streamable HTTP, no key); the API and MCP docs show how to connect Claude, Cursor or VS Code.

From a national account number: GET /api/v1/iban/check-digits?country=GB&bban=… or the MCP tool compute_iban_check_digits computes the check digits and the whole IBAN.

Other 22-character IBANs

The same length doesn’t mean the same structure: compare the BBAN formats. All IBAN formats and lengths

Source: the SWIFT IBAN Registry (ISO 13616), transcribed and checked against each country’s registry example; the positions of bank and branch codes are given only where the registry’s are well established. The SWIFT IBAN Registry is the authority. Informational only.