Japan My Number Validator

The Japanese individual number, commonly called My Number (個人番号), is a 12-digit identifier assigned to every resident of Japan. It links a person’s tax, social-security and disaster-response records, and employers collect it for payroll withholding. The twelfth digit is a check digit, so a single mistyped or transposed digit can be detected. This free validator runs the official algorithm so you can catch errors before a filing is rejected.

How it works

Japan’s My Number uses a backward-weighted modulo-11 check digit. The eleven payload digits (everything except the rightmost check digit) are numbered 1 to 11 starting from the lowest (rightmost) payload position:

1. Assign each payload digit Pn a weight Qn: for positions 1 to 6, Qn = n + 1; for positions 7 to 11, Qn = n - 5.
2. Compute the weighted sum of Pn × Qn.
3. Take that sum modulo 11.
4. If the remainder is 0 or 1, the check digit is 0. Otherwise the check digit is 11 - remainder.

The number is valid when this computed check digit equals the actual twelfth digit. The tool shows the weighted sum, the remainder and the expected check digit so the result is fully transparent.

How it works in practice

Suppose the payload digits and their weights produce a weighted sum whose remainder modulo 11 is 4. Then the expected check digit is 11 - 4 = 7, and the number is valid only if its last digit is 7. If the remainder were 1, the expected check digit would be 0.

Tips and notes

• A failed check almost always means a digit was typed wrong or transposed. Re-check all 12 digits against the source document.
• My Number is highly sensitive personal data under Japan’s My Number Act. This tool processes everything locally and sends nothing anywhere.
• A valid checksum is necessary but not sufficient — it never proves the number belongs to a specific person.