# UK IBAN Validator & Sort Code Checker (Bacs & CHAPS)
> Instant MOD-97 validation for 22-character United Kingdom IBANs with 6-digit sort code and 8-digit account number extraction.

- **Canonical URL:** https://stanzaapi.com/tools/iban-validator/country/united-kingdom-gb
- **Governing Standard:** ISO 13616 / ISO 7064 MOD-97-10 (SWIFT & ISO 13616 IBAN Registry)
- **Latency:** <1ms Edge
- **Privacy:** In-memory execution only (zero data stored or logged)

## Technical Overview & Governing Rules
In United Kingdom, the International Bank Account Number (IBAN) has a fixed length of 22 alphanumeric characters starting with the two-letter ISO 3166-1 alpha-2 country code 'GB', followed by two MOD-97 check digits.

The National Basic Bank Account Number (BBAN) follows the official pattern: 4a14n. The national bank code is located at BBAN character offset [0:4]. The branch identifier is at offset [4:10].

National IBAN transfers in United Kingdom (GB) are settled in GBP.

Validation computes the ISO 7064 Modulo-97-10 checksum by transposing the first 4 characters to the end, converting letters to numeric digits (A=10, ..., Z=35), and calculating arithmetic integer modulo 97 (must equal 1).

## Specification Matrix
| Attribute | Value | Description |
| --- | --- | --- |
| Country Code | GB | ISO 3166-1 alpha-2 |
| Total IBAN Length | 22 characters | Fixed standard length |
| BBAN Format | 4a14n | National structure (n=numeric, a=alpha, c=alphanumeric) |
| SEPA Zone | Yes (Single Euro Payments Area) | SEPA compliance status |
| Currency (ISO 4217) | GBP | National settlement currency |
| Bank Code Position | BBAN Offset 0 (4 chars) | National clearing code |
| Branch Code Position | BBAN Offset 4 (6 chars) | Branch identification |

## Standard JSON Response Model
```json
{
  "valid": true,
  "iban": "GB00...",
  "countryCode": "GB",
  "countryName": "United Kingdom",
  "length": 22,
  "bban": "4a14n",
  "sepa": true,
  "checksumValid": true,
  "bankCode": "XXXX"
}
```

## Frequently Asked Questions & Edge Cases
### Q: How many characters is an IBAN in United Kingdom?
**A:** An official IBAN in United Kingdom (GB) is exactly 22 characters in length. Any shorter or longer value fails ISO 13616 validation.

### Q: Is United Kingdom part of the SEPA payment network?
**A:** United Kingdom is a member of the Single Euro Payments Area (SEPA), enabling low-cost euro bank transfers.

### Q: What currency are United Kingdom IBAN transfers settled in?
**A:** IBAN transfers for United Kingdom (GB) settle in GBP, the national settlement currency. Cross-border SEPA transfers to United Kingdom may still be denominated in EUR where both banks support the scheme.

### Q: How is the MOD-97 check digit calculated for GB IBANs?
**A:** The first 4 characters are moved to the end, letters are converted to numbers (A=10 to Z=35), and the resulting number is evaluated with modulo 97 arithmetic. A valid IBAN yields a remainder of exactly 1.