Japan Invoice Registration Number Validator | T-Number Check Digit Verification
Verify the format, "T" prefix, and check digit of a Japanese Qualified Invoice Issuer registration number (T-number) entirely offline in your browser. Quickly spot typos before they cause invoice problems.
What is this Invoice Registration Number Validator?
A Qualified Invoice Issuer registration number, commonly called a "T-number," is required under Japan's Invoice System (Qualified Invoice Retention Method), which began in October 2023, in order for buyers to claim input consumption tax credits. It consists of "T" followed by 13 digits; for corporations, those 13 digits are identical to the corporation's existing Corporate Number. When you receive an invoice from a supplier and need to re-key its registration number into your accounting system, being able to quickly catch a dropped or transposed digit saves real bookkeeping time.
This tool computes the check digit (the last digit) from the first 12 digits using the same algorithm published by Japan's National Tax Agency, and confirms whether it matches the digit actually entered. Nothing you type is sent to any server — all calculations run locally in your browser via JavaScript. Keep in mind this tool can only confirm that a number is *formatted* correctly; it cannot confirm that the business is actually registered as a Qualified Invoice Issuer, or that the registration is still active. For that, please use the National Tax Agency's official lookup site.
How to use this tool
- Enter the invoice registration number Type in the 13-digit number starting with "T" exactly as it appears on the invoice. Spaces and hyphens are removed automatically.
- Check the format result See whether the number matches the required "T" + 13 digits format.
- Check the check digit result See whether the last digit matches the value computed from the first 12 digits. If it does not match, the correct check digit is also shown as a hint for finding the typo.
Tips for getting more out of it
- Pasted numbers with spaces or hyphens are automatically cleaned up before validation, so you can paste them exactly as copied.
- For corporations, the registration number is simply "T" plus the existing 13-digit Corporate Number, so cross-checking against the Corporate Number lookup service (if available) can improve accuracy.
- Sole proprietors and unincorporated associations do not have a pre-existing Corporate Number, so a new 13-digit number is assigned when they register — but the same check digit algorithm is used regardless.
- This result is for reference only. For any decision that matters (such as claiming a tax credit), always confirm actual registration status on the National Tax Agency's official lookup site.
Where this is useful
Catching typos when re-keying a supplier's invoice number
Quickly confirm there are no dropped or transposed digits when copying a registration number from a received invoice into your accounting system.
Double-checking your own number before issuing invoices
Confirm your own registration number is correctly formatted when setting it up in a new invoice template.
First-pass screening for accounting staff handling many suppliers
Use this as a quick first-pass filter for obvious typos before running an official lookup on the National Tax Agency site.
Bulk sanity-checking during a billing system migration
When migrating to a new invoicing system, check that registration numbers already stored in your supplier master data are correctly formatted.
Glossary
- Invoice Registration Number (T-Number)
- A registration number proving a business is a Qualified Invoice Issuer under Japan's Invoice System. It consists of "T" followed by 13 digits.
- Check digit
- A verification digit appended to a number to detect input errors. It is valid when it matches the value computed from the other digits using a fixed formula.
- Corporate Number
- A 13-digit number assigned by Japan's National Tax Agency to every corporation. A corporation's invoice registration number is identical to its Corporate Number with "T" prepended.
- Invoice System (Qualified Invoice Retention Method)
- Japan's consumption tax input credit system that began in October 2023. To claim an input tax credit, a buyer generally must retain a Qualified Invoice issued by a registered Qualified Invoice Issuer, showing the registration number.
- Qualified Invoice Issuing Businesses lookup site
- An official site run by Japan's National Tax Agency where anyone can look up a registered business's name and registration date from its registration number. Use it for final confirmation of actual registration status.
Frequently asked questions
Side Note — How the T-number borrows from the Corporate Number
When Japan's Invoice System launched, many accountants were surprised to learn that a corporation's new invoice number was not, in fact, a brand-new identifier. It was simply the Corporate Number — a 13-digit number every Japanese corporation had already been assigned back in 2015 — with a single letter "T" tacked on the front. Rather than building an entirely new numbering system from scratch, the National Tax Agency reused the existing Corporate Number registry, which meant corporations did not need to memorize a new number, and existing invoicing and accounting software required only minor changes to accommodate the new prefix.
Sole proprietors, freelancers, and unincorporated associations (certain organizations like PTAs or alumni groups), however, have no underlying Corporate Number to borrow from. For them, a fresh 13-digit number is minted for the first time only when they apply for Invoice System registration. Even for these newly minted numbers, the check digit is computed using the exact same algorithm as for corporations — so there is no way to tell, just by looking at the digits, whether a number was inherited from an existing Corporate Number or assigned fresh.
The idea of a check digit itself is a classic trick shared with postal codes, ISBNs, and credit card numbers: a simple mechanical way to catch the most common kinds of human transcription errors — a single mistyped digit, or two adjacent digits swapped — without any complex verification. The Corporate Number algorithm achieves this with a fairly simple modular arithmetic scheme: each of the 12 base digits is weighted according to its position, the weighted values are summed, and the check digit is derived from the remainder after dividing by 9. No cryptography required — just enough arithmetic to catch the everyday typo.