Japan Corporate Number Validator

Every company, government body and registered organisation in Japan carries one public 13-digit identifier: the corporate number (法人番号, hōjin bangō), assigned by the National Tax Agency under the 2013 My Number Act. Unlike the personal My Number, it is deliberately public — searchable by anyone in the NTA’s corporate number publication site. Its first digit is a check digit, which means a single mistyped or transposed digit is mathematically detectable before you ever query the registry. This validator runs that official check locally in your browser.

Anatomy of the 13 digits

Because the base of a company’s corporate number is its commercial registry number, the corporate number links the tax identity and the corporate registry identity of the same entity — one of the design goals of the system.

The official check-digit algorithm

Number the 12 base digits 1 to 12 starting from the rightmost digit. Then:

weight Qn = 1  when position n is odd
         = 2  when position n is even
sum   = Σ (digit at position n) × Qn
check = 9 − (sum mod 9)

The number is valid when this computed value equals the actual first digit. Note a subtlety of the formula: check ranges from 1 to 9 — a corporate number can never begin with 0, because 9 − (sum mod 9) never yields zero. That is itself a quick sanity check: any 13-digit “corporate number” starting with 0 is invalid on sight.

Worked example, digit by digit

Take the base 010401089914 (positions 12 down to 1, left to right):

Weighted sum = 47. Then 47 mod 9 = 2, and the check digit is 9 − 2 = 7. The full valid corporate number is therefore 7010401089914. If an invoice showed 8010401089914, the validator would flag it immediately — some digit was misread or mistyped.

Why validation matters since the invoice system

Japan’s qualified invoice system (適格請求書等保存方式, the “invoice seido”) took effect on 1 October 2023. To claim input credits for consumption tax, a business must hold qualified invoices showing the supplier’s invoice registration number — the letter T followed by the supplier’s 13 digits, e.g. T7010401089914. Details are on the NTA’s invoice-system pages, and registered issuers can be confirmed on the qualified invoice issuer publication site.

The practical workflow accounting teams have converged on:

1. Checksum first (this tool) — catches transcription errors instantly, offline, before any lookup.
2. Registry lookup second — confirm the entity exists and matches the supplier’s name at houjin-bangou.nta.go.jp.
3. Invoice-issuer lookup third — confirm the T number is an active registered issuer, since registration can be revoked or surrendered.

A checksum-valid number that fails step 3 is the case that costs money: the invoice will not support an input-tax credit.

What the check digit can and cannot catch

The alternating 1-2 weighting over modulo 9 detects all single-digit errors except substitutions that differ by 9 in weighted value — in practice nearly every typo — and most adjacent transpositions (swapping two neighbouring digits changes the weighted sum unless the two digits are equal or their difference is a multiple of 9 under the weight swap). It cannot detect a completely different but internally valid number, a valid number attached to the wrong company, or a deregistered entity. Structural validity is necessary, never sufficient.

Edge cases

Branches have no separate number — one corporate number covers the whole legal entity, unlike some countries’ per-establishment IDs. Sole proprietors have no corporate number at all; their invoice registration numbers are T + a 13-digit NTA-assigned number that deliberately does not reveal their My Number — such numbers still pass the same checksum. Dissolved companies keep their number in the registry with a closure record, so an old invoice can still be cross-checked. And when pasting from Japanese documents, watch for full-width digits (１２３…) — convert them to half-width ASCII digits before validating; this tool accepts both.

Sources

• NTA Corporate Number Publication Site (法人番号公表サイト)
• NTA — qualified invoice system (インボイス制度)
• Qualified Invoice Issuer Publication Site

Everything runs locally in your browser — nothing you type is uploaded. A valid checksum confirms internal consistency only; always confirm the entity in the official registry for due-diligence purposes.