How to Validate a Korean Business Registration Number — Free Format & Checksum Check
Jun 23, 2026
About to sign a contract with a new supplier and want to double-check their business registration number? A single wrong digit can get a tax invoice rejected or make a contract reference invalid. This guide explains the structure of a Korean business registration number and how to quickly verify that the format is correct — no installation or sign-up needed.
Enter a 10-digit business registration number and get an instant format and checksum result. Free, no sign-up.
Validate Business Number →Business Registration Number Structure — What Each Digit Means
A Korean business registration number is always 10 digits, formatted as XXX-XX-XXXXX. Every segment carries specific information.
| Segment | Digits | Meaning |
|---|---|---|
| First 3 digits | XXX- | Regional tax office code |
| Middle 2 digits | -XX- | Taxpayer type (individual, corporation, etc.) |
| Next 4 digits | -XXXX | Serial number |
| Last 1 digit | -XXXXX(last) | Check digit — computed from the first 9 digits |
The final digit is a check digit derived from a weighted calculation of the preceding 9 digits. If this digit doesn't match, the number has been entered incorrectly.
How to Validate — 2 Steps
- Enter the number — Go to Business Number Validator and type in the 10 digits. Hyphens are optional.
- Read the result — If the digit count and check digit are both correct, the number is shown as a valid format. If not, you'll see exactly what's wrong.
Format Validation vs. Live Registry Lookup — Know the Difference
This tool checks whether the format and checksum of the number are correct. It does not query whether the business is actually registered with the National Tax Service, currently operating, or has closed.
| What you want to know | FreeSign Tool | NTS Hometax |
|---|---|---|
| 10-digit format is correct | ✔ | ✔ |
| Check digit is valid | ✔ | ✔ |
| Business is registered with NTS | ✘ | ✔ |
| Business is active / suspended / closed | ✘ | ✔ |
In short: use FreeSign to quickly check whether a number is correctly formed, and use NTS Hometax when you need to verify the actual registration status (active, suspended, or closed).
Related Tools
Once you've confirmed the business number and are ready to proceed, you can send a signing request directly via FreeSign e-signature. If the other party is an individual and you need to check their ID number format, the Resident Registration Number Validator works the same way.
Frequently Asked Questions
Q. The tool says the format is valid — does that mean the business actually exists?
No. This tool only checks whether the 10-digit structure and check digit follow the correct rules. To confirm the business is actually registered, use the National Tax Service Hometax portal separately.
Q. Can I enter the number without hyphens?
Yes. Both 123-45-67890 and 1234567890 are accepted — the tool handles either format.
Q. How is the check digit calculated?
Each of the first 9 digits is multiplied by a fixed weight (1, 2, 1, 2, 1, 2, 1, 2, 1 respectively), the products are summed, and the remainder from a specific formula is compared against the last digit. The math is involved — that's why the tool exists.
Q. Is this free? Is the number I enter stored anywhere?
It's free. The number is validated entirely in your browser and is never sent to or stored on our servers.