Pattern

Regex for UK postcode

UK postcode in either compact or spaced form.

The pattern

^[A-Z]{1,2}\d[A-Z\d]?\s?\d[A-Z]{2}$

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What it matches

SW1A 1AA
M1 1AE
B33 8TH
CR0 6XH
EC1A 1BB

What it doesn't match

12345
SW1A
SW1A 1A
SW1A1AAA

Notes & gotchas

UK postcodes have an area+district half and a sector+unit half, optionally separated by a space. Format varies (A1 1AA, A1A 1AA, AA1 1AA, AA1A 1AA, AA11 1AA, etc.) but this pattern covers all common forms.

Code in your language

Use the explainer's Code tab to generate ready-to-paste snippets in JavaScript, Python, Java, .NET, Go, Ruby, and PHP for this pattern.

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About this pattern

UK identifier formats are set by HMRC, Royal Mail, and the BACS payments scheme. The regex here matches the format; full validation may need an additional checksum or lookup.

Quick usage in different languages

Once you've validated a candidate value matches this pattern, you'll typically use it inside your application code. Each language has its own regex syntax:

JavaScript: new RegExp(pattern).test(value)
Python: re.match(pattern, value) with raw strings: r"pattern"
Java: Pattern.compile(pattern).matcher(value).matches()
C# / .NET: Regex.IsMatch(value, pattern)
Go: regexp.MustCompile(pattern).MatchString(value) — Go uses RE2 so some advanced features aren't available
Ruby: value =~ /pattern/ or pattern.match?(value)
PHP: preg_match('/pattern/', $value)

The explainer's Code tab generates these for any pattern you paste — including the right escaping and idioms for each language.

Common pitfalls

Anchors matter. If the pattern uses ^ and $ it expects the entire input to match. To find this pattern inside a longer text, remove the anchors and use the /g flag.
Case sensitivity. Letter ranges like [A-Z] only match uppercase. Use the i flag or [A-Za-z] for case-insensitive matching.
Escape user input. If you're building a regex from a string variable, escape regex metacharacters first to avoid bugs or injection.
Performance. For this specific pattern the risk is low, but be cautious of nested quantifiers when adapting it — they can cause exponential backtracking on adversarial input.