How many digits is a Korean BRN?

A South Korean business registration number is exactly 10 digits, normally written in the pattern XXX-XX-XXXXX. The first three digits are the tax-office code, the next two the taxpayer type, the next four a serial, and the last is the check digit.

How is the BRN check digit calculated?

The first nine digits are multiplied by the weights 1,3,7,1,3,7,1,3,5. An extra term adds the tens-carry from multiplying the ninth digit by 5. The products are summed, and the check digit is 10 minus the sum modulo 10, taken modulo 10 again.

Why is there an extra carry term for the ninth digit?

The ninth digit is multiplied by 5, which can produce a two-digit product. The official algorithm adds the tens portion of that product (floor of the product over ten) back into the sum, so the calculation differs from a plain weighted modulo.

Does a valid check digit mean the business is active?

No. A valid check digit only confirms the number is internally consistent. To confirm the business is currently registered and trading, look it up on the National Tax Service Hometax portal. This tool performs no online lookup.

What is the difference between a BRN and a corporate number?

The 10-digit business registration number identifies a taxpaying business and is used for invoicing and e-Tax. The separate 13-digit corporate registration number is issued by the court registry for incorporated companies. They are not interchangeable.

South Korea Business Registration Number Validator

A South Korean business registration number (사업자등록번호) is the 10-digit tax identifier every business needs for invoicing, e-Tax filing and public procurement. This validator runs the official National Tax Service check algorithm entirely in your browser, so you can confirm a supplier’s number is well-formed before trusting it.

How it works

The 10 digits split into a tax-office code (1–3), a taxpayer-type code (4–5), a serial number (6–9) and a check digit (10). The check digit uses a weighted modulo-10 scheme with a special carry step:

Multiply the first nine digits by the weights 1, 3, 7, 1, 3, 7, 1, 3, 5.
Add an extra term: the tens-carry from the ninth product, i.e. floor((ninth digit × 5) / 10).
Sum everything.
The check digit is (10 − (sum mod 10)) mod 10.

If that value equals the tenth digit, the number is internally consistent.

Notes

The carry term on the ninth digit is what distinguishes the Korean algorithm from a plain weighted modulo-10 check; omitting it gives wrong results for many real numbers. A passing check digit confirms format only, not active registration — use Hometax to confirm a business is trading. All processing here is local.