Regex builder

Pattern

^(?:\d{4})-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])$

Piece-by-piece explanation

• ^ — Start of the string.
• \d{4} — Exactly four digits for the year.
• - — Literal hyphen.
• (?:0[1-9]|1[0-2]) — Month from 01 through 12.
  • 0[1-9] matches 01–09.
  • 1[0-2] matches 10–12.
• - — Literal hyphen.
• (?:0[1-9]|[12]\d|3[01]) — Day from 01 through 31.
  • 0[1-9] matches 01–09.
  • [12]\d matches 10–29.
  • 3[01] matches 30–31.
• $ — End of the string.

Matching examples

2026-07-02
1999-12-31
2000-01-01
0001-09-09
9999-11-30

Non-matching examples

2026-7-02       # Month is not two digits
2026-07-2       # Day is not two digits
26-07-02        # Year is not four digits
2026-13-01      # Invalid month
2026/07/02      # Wrong separator

Common pitfalls

• This regex validates the format and basic month/day ranges, but not actual calendar validity. For example, it matches:
  • 2026-02-31
  • 2025-04-31
  • 2025-02-29
• Use a date parser or additional validation if leap years and month-specific day limits matter.
• \d may match Unicode digits in some regex engines. To require ASCII digits only, use:

^[0-9]{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12][0-9]|3[01])$

• Multiline mode can change the behavior of ^ and $, allowing matches at line boundaries rather than only at the boundaries of the entire input.

PCRE compatibility

Supported as written:

\A[0-9]{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12][0-9]|3[01])\z

\A and \z provide strict whole-string anchoring in PCRE.

JavaScript compatibility

Supported as written:

const pattern = /^[0-9]{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12][0-9]|3[01])$/;

Avoid the m flag if the entire input must be one date.

Python compatibility

Supported with re.fullmatch, which is preferable for whole-string validation:

import re

pattern = re.compile(
    r"[0-9]{4}-