Business Number Validation

Validates Korean business registration numbers offline using the National Tax Service standard checksum algorithm. Auto-classifies entity type by middle digits. Operating status requires external API.

Validation Result

Enter a business registration number and click Validate.

What this tool does

The Korean business registration number validator instantly verifies the checksum of a 10-digit business number to catch typos and fabricated numbers. Verification uses the National Tax Service's published 1-3-7-1-3-7-1-3-5 weight algorithm and runs entirely in your browser — no server call, no data leaves your device. Use it as a safety check before transactions, contracts, or wire transfers.

Who uses this

Vendor onboarding: validate format before issuing tax invoices
Wire transfer safety: verify the recipient's business number format in one second
Accounting systems: catch input errors and fabricated numbers in ERP
Foreign accountants and counsel: quick validation when you don't know Korean format rules
E-tax invoice manual entry: digit count and checksum verification before issuance

How to use (3 steps)

1Enter the 10-digit business registration number — digits only or with hyphens (e.g., 123-45-67890). Format normalizes automatically.
2Checksum verification runs instantly. Result displays as Pass (green) or Format Error (red).
3A Pass does not guarantee an active business. For real-time registration status, check Hometax's 'Business Status Inquiry' separately.

Checksum algorithm (Korean NTS standard)

Let the 10 digits be d1·d2·...·d10: 1) Multiply the first 9 digits by weights 1-3-7-1-3-7-1-3-5 and sum sum = d1×1 + d2×3 + d3×7 + d4×1 + d5×3 + d6×7 + d7×1 + d8×3 + d9×5 2) Add the tens digit of (d9 × 5) sum += floor(d9 × 5 / 10) 3) Check digit = (10 − sum % 10) % 10 4) If the check digit equals d10, the number passes The middle two digits (d4·d5) indicate business type (individual 01~79, corporation 81/86/87, non-profit 82, etc.) — informational, not part of validation.

Real examples

Example 1: 123-45-67890 — catching a fake number

Checksum: (1×1 + 2×3 + 3×7 + 4×1 + 5×3 + 6×7 + 7×1 + 8×3 + 9×5) + floor(9×5/10) = 169. (10 − 169%10) % 10 = 1. Digit 10 is 0, not 1 → Format error. Fake.

Example 2: NTS standard test number — passes

Sample numbers in the National Tax Service manual pass the checksum. The tool shows 'Valid' immediately. Active registration still needs separate confirmation.

Example 3: Identifying business type from middle digits

XXX-81-XXXXX = for-profit corporation. XXX-82-XXXXX = non-profit. XXX-01~79-XXXXX = individual sole proprietor. You can identify the counterparty's legal form at a glance.

Frequently asked questions

Does passing the checksum mean an active business?

No. The checksum only verifies format. For actual registration and operating status, check Hometax's 'Business Registration Status Inquiry' (no certificate required). Use this tool as the first-pass format filter.

Why the 1-3-7 weights?

It's a variant of ISO 7064 adopted by the Korean National Tax Service in 1976. The 1·3·5·7 weight combination catches nearly all single-digit typos and adjacent-digit transpositions.

What do the middle two digits mean?

Business type code: 01~79 = individual sole proprietor, 80 = MLM individual, 81·86·87 = for-profit corporation, 82 = non-profit, 83 = government, 84 = foreign corporation, 89 = HQ, 90~99 = branch offices.

Can foreign counterparties validate Korean business numbers?

Yes. This tool runs entirely in the browser without internet or server calls, so it works the same way from outside Korea. Use it for format validation before signing with a Korean company.

Do Korean resident registration numbers have a similar checksum?

Yes, the 13-digit resident registration number has its own checksum. This tool is business-number-only; resident number validation requires a separate tool.

Can I validate corporate registration numbers (법인등록번호)?

Business registration number (10-digit) and corporate registration number (13-digit) are different. The corporate number uses a different checksum issued by the court registry. This tool only supports business registration numbers.

Cautions

•Checksum pass = format valid. Actual registration/operating status requires separate Hometax check.
•Middle digits identify individual/corporation, but cannot tell you suspension or closure status.
•This tool runs entirely in the browser — no input is sent externally.
•E-tax invoice issuance requires both format validation and active registration confirmation.