Invoice Number Regex for PHP

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching invoice number, ported and verified for PHP. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Invoice Number
// ReDoS-safe | RegexVault — Finance > Financial Formats

define('INVOICE_NUMBER_PATTERN', '/^[A-Z0-9\-]{4,15}$/');

function validate_invoice_number(string $input): bool {
    return (bool) preg_match(INVOICE_NUMBER_PATTERN, $input);
}

// Example
var_dump(validate_invoice_number("INV-00001")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Financial Formats category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Invoice numbering conventions vary widely. This pattern covers the most common formats. The prefix identifies the document type (INV, SINV, PO, CN for credit note). Pad with leading zeros for sortability.