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.

Last reviewed: 2026-05-23