BTSDB Guide · Business — reading the 10 digits like a local
Every registered business in Korea — from Samsung to a one-person online shop — has a unique 10-digit 사업자등록번호 (business registration number), written as 123-45-67890. It's the closest thing Korea has to a public company ID, and the digits aren't random: they tell you who issued it, what kind of entity you're dealing with, and whether the number itself is even plausible.
Example: 120-88-00767 (Coupang) has "88" in the middle — a for-profit corporation's head office. A supplier claiming to be a large corporation whose number shows 01–79 is a sole proprietor, which changes your contract counterparty and risk profile.
The final digit is derived mathematically from the first nine (weights 1-3-7-1-3-7-1-3-5, plus a correction term). Around 90% of random or mistyped 10-digit strings fail it. The BTSDB checker validates the checksum instantly and then confirms with the National Tax Service whether the number is actually registered — passing the checksum alone doesn't mean the business exists.
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|
| Digit | 1 | 2 | 0 | 8 | 8 | 0 | 0 | 7 | 6 |
| Weight | 1 | 3 | 7 | 1 | 3 | 7 | 1 | 3 | 5 |
| Product | 1 | 6 | 0 | 8 | 24 | 0 | 0 | 21 | 30 |
The products add up to 90. Take the ninth digit (6), multiply by 5 and keep the tens digit of the result (30 → 3), giving 93. The remainder after dividing by 10 is 3, and (10 − 3) mod 10 = 7 — the last digit of the number. It passes.
function isValidKoreanBizNo(input) {
const d = String(input).replace(/\D/g, '');
if (d.length !== 10) return false;
const w = [1, 3, 7, 1, 3, 7, 1, 3, 5];
let sum = 0;
for (let i = 0; i < 9; i++) sum += Number(d[i]) * w[i];
sum += Math.floor(Number(d[8]) * 5 / 10);
return (10 - (sum % 10)) % 10 === Number(d[9]);
}One company can also hold several business registration numbers: registration is per place of business, and a corporate branch gets its own number with 85 in the middle. Make sure the number on your contract belongs to the office that is signing.
Related: 5-step company verification · Types of Korean companies
Ten, written as 3-2-5: for example 120-88-00767. The first three identify the issuing tax office, the middle two the type of entity, and the last five are a serial number ending in a check digit.
No. It only shows the digits are internally consistent. Whether the number is actually registered, and whether the business is active, has to be confirmed with the National Tax Service lookup.
No. The corporate registration number has 13 digits and is issued by the court registry at incorporation. The business registration number has 10 digits and is issued by the tax office.
Yes. Registration is made for each place of business, so a company with several sites can hold several numbers. A corporate branch has 85 as its middle two digits.
They show which tax office first issued the number. The number does not change when a business moves, so it may not match the current address.