Regex to Match YYYY-MM-DD Dates

This regex validates dates in the YYYY-MM-DD format, which is the ISO 8601 standard. Here is the token-by-token breakdown:

^ — Anchors the match at the start of the string.

\d{4} — Matches exactly four digits for the year. This accepts any four-digit year from 0000 to 9999.

• — Matches a literal hyphen separating the year from the month.

(?:0[1-9]|1[0-2]) — A non-capturing group with two alternatives for valid months (01-12). 0[1-9] matches months 01-09, and 1[0-2] matches months 10-12. This prevents invalid months like 00 or 13.

• — Matches a literal hyphen separating the month from the day.

(?:0[1-9]|[12]\d|3[01]) — A non-capturing group with three alternatives for valid days (01-31). 0[1-9] matches days 01-09, [12]\d matches days 10-29, and 3[01] matches days 30-31. This prevents invalid days like 00 or 32.

$ — Anchors the match at the end of the string.

This pattern validates the format and basic ranges but does not account for month-specific day limits. For example, it would accept 2024-02-31 even though February never has 31 days. For full calendar validation, combine this regex with programmatic checks for month lengths and leap years. The ISO 8601 date format is widely used in databases, APIs, and international data exchange because it is unambiguous and sorts chronologically.