Pattern

Regex for US ABA routing number

9-digit bank routing/ABA transit number.

The US ABA routing number regex is ^\d{9}$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^\d{9}$

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What it matches

021000021
111000025

What it doesn't match

12345
12345678
1234567890

Notes & gotchas

9 digits. The first 2 indicate Federal Reserve district. ABA routing numbers have a checksum — validate it in code: 3*(d1+d4+d7) + 7*(d2+d5+d8) + (d3+d6+d9) ≡ 0 (mod 10).

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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Token-by-token breakdown

Every part of the pattern, left to right:

Token	Meaning
`^`	start of string (or line in multiline mode)
`\d{9}`	exactly 9 times: digit (0–9)
`$`	end of string (or line in multiline mode)

About this pattern

US-specific identifiers follow patterns set by federal and state authorities (SSA, IRS, USPS, state DMVs). Regex catches malformed values; final validation usually requires an authoritative lookup.

Quick usage in different languages

This exact pattern — with the correct escaping and idioms for each language:

JavaScript: /^\d{9}$/.test(value)
Python: re.match(r"^\d{9}$", value)
Java: Pattern.compile("^\\d{9}$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^\d{9}$")
Go: regexp.MustCompile(`^\d{9}$`).MatchString(value)
Ruby: /^\d{9}$/.match?(value)
PHP: preg_match('~^\d{9}$~', $value)

The explainer’s Code tab regenerates these for any pattern you paste, and the downloadable cheat sheet bundles the breakdown, all seven snippets, and the pitfalls below onto one printable page.

Common pitfalls

Anchored to the whole string. This pattern uses ^ and $, so it requires the entire input to match. To find it inside a longer text, drop the anchors and use the global (g) flag.
Escape it correctly per language. In Java and JavaScript strings each backslash must be doubled (\\d); in Python, Go, and C# use raw/verbatim strings so the backslashes survive.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the us aba routing number against a source of truth (database, API, or checksum) where it matters.

Standards & sources

This pattern is based on the following authoritative specification(s) and issuing authorities. Formats can change — always confirm against the primary source.

American Bankers Association — routing numbers

Related patterns

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