Accounting Format (Negative in Parentheses) Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching accounting format (negative in parentheses), 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
// Accounting Format (Negative in Parentheses)
// ReDoS-safe | RegexVault — Finance > Currency & Money

define('ACCOUNTING_FORMAT_NEGATIVE_IN_PARENTHESES_PATTERN', '/^(?:\((?:(?:[1-9][0-9]*(?:,[0-9]{3})*)|0)(?:\.[0-9]{1,2})?\)|(?:(?:[1-9][0-9]*(?:,[0-9]{3})*)|0)(?:\.[0-9]{1,2})?)$/');

function validate_accounting_format_negative_in_parentheses(string $input): bool {
    return (bool) preg_match(ACCOUNTING_FORMAT_NEGATIVE_IN_PARENTHESES_PATTERN, $input);
}

// Example
var_dump(validate_accounting_format_negative_in_parentheses("1,234.56")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Currency & Money 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

Standard accounting/financial statement format. Parentheses denote debit or loss depending on context. Strip parentheses and negate when converting to numeric type for calculation.