What is a South Korean RRN?

A Resident Registration Number (주민등록번호, RRN) is a 13-digit national ID issued by the Korean Ministry of the Interior and Safety. It encodes the holder's birth date, a gender/century code that also distinguishes Korean nationals from foreign nationals, a four-digit serial, and a single check digit. Every South Korean national receives one at birth; foreign residents registered under the Foreigner Registration system receive an equivalent number with gender codes 5–8.

How is the check digit calculated?

Multiply each of the first 12 digits by the corresponding weight from the fixed sequence [2, 3, 4, 5, 6, 7, 8, 9, 2, 3, 4, 5], sum the products, compute sum mod 11, subtract from 11, then take the result mod 10. Formally: check = (11 − (sum mod 11)) mod 10. If the 13th digit of the number matches this value the checksum passes.

What does the gender/century code digit mean?

The 7th digit (first digit after the hyphen) encodes both the birth century and the holder's nationality. Codes 1/2 mean male/female born 1900–1999 (Korean national). Codes 3/4 mean male/female born 2000–2099. Codes 5/6 mean male/female foreign nationals born 1900–1999. Codes 7/8 cover foreign nationals born 2000–2099. Codes 9/0 cover the rare 1800s births.

Why does the tool show the full four-digit birth year?

The first two digits of an RRN record only the two-digit year (YY). The birth century is determined by the gender code digit, so the same YY of "85" means 1985 for code 1 or 2, but 2085 for code 3 or 4. The validator reads the gender code first, adds the correct century, and displays the unambiguous four-digit year.

Does a "valid" result mean the number is registered?

No. Passing the checksum and having a plausible birth date confirms the number is structurally correct — it could have been legitimately issued. It does not query any Korean government database, so it cannot confirm the number is active, belongs to a real person, or has not been cancelled.

Is it safe to paste a real RRN here?

The validator is entirely client-side JavaScript. No data is sent to any server, stored in any database, or logged anywhere. You can verify this by disabling your network connection before using the tool — it still works. That said, be cautious about pasting real government ID numbers into any website, and use an obviously-fake test number where possible.

South Korea RRN Validator

The South Korean Resident Registration Number (주민등록번호, often abbreviated RRN or JuminDeungnokBeonho) is a 13-digit national identifier issued by the Korean Ministry of the Interior and Safety to every Korean citizen at birth, and to registered foreign residents under a parallel scheme. If you are building a Korean-market application, integrating with Korean payment gateways, processing KYC data, or working with government APIs, you will encounter RRNs regularly — and you need a way to catch typos and malformed numbers before they reach your database.

This tool runs the official weighted mod-11 check-digit algorithm entirely in your browser, extracts the embedded birth date (with an unambiguous four-digit year), decodes the gender and nationality indicator, and shows you every intermediate step so you understand why a number passes or fails.

Structure of an RRN

An RRN follows the pattern YYMMDD-GXXXXC:

Position	Length	Meaning
1–2	2 digits	Birth year, last two digits (YY)
3–4	2 digits	Birth month (01–12)
5–6	2 digits	Birth day (01–31)
7	1 digit	Gender / century / nationality code (G)
8–11	4 digits	Serial: encodes original registration region + sequence (XXXX)
12	1 digit	Historically encoded sub-region; now mostly redundant
13	1 digit	Check digit (C)

The hyphen after position 6 is conventional; it is not part of the number itself and this validator accepts input with or without it.

Gender and century codes

The single digit at position 7 is the most information-dense field in the RRN:

Code	Gender	Birth century	Nationality
9	Male	1800s	Korean national
0	Female	1800s	Korean national
1	Male	1900s	Korean national
2	Female	1900s	Korean national
3	Male	2000s	Korean national
4	Female	2000s	Korean national
5	Male	1900s	Foreign national
6	Female	1900s	Foreign national
7	Male	2000s	Foreign national
8	Female	2000s	Foreign national

Codes 9 and 0 exist for historical records only. The overwhelming majority of RRNs in active use carry codes 1–4.

The mod-11 check-digit algorithm

The check digit at position 13 is computed from the preceding 12 digits using a fixed weight sequence and modular arithmetic:

Weights (fixed, repeating): [2, 3, 4, 5, 6, 7, 8, 9, 2, 3, 4, 5]
Weighted sum: multiply each digit by its corresponding weight and add them all up.
Remainder: compute weightedSum mod 11.
Subtract: 11 − remainder.
Final mod: take the result mod 10 to produce a single digit.

Concisely: check = (11 − (weightedSum mod 11)) mod 10

The final mod 10 step handles the case where step 4 yields 10 or 11 — both reduce to a single digit (0 or 1) so the check digit is always in the range 0–9.

Example (obviously fake, for illustration)

Consider the fake number 850312-1234567. Breaking it down:

Birth date digits: 8 5 0 3 1 2
Gender/century code: 1 (male, born 1900s → birth year 1985-03-12)
Serial digits: 2 3 4 5
Sub-region digit: 6
Check digit: 7

Weighted sum = (8×2)+(5×3)+(0×4)+(3×5)+(1×6)+(2×7)+(1×8)+(2×9)+(3×2)+(4×3)+(5×4)+(6×5) = 16+15+0+15+6+14+8+18+6+12+20+30 = 160

160 mod 11 = 6 → 11 − 6 = 5 → 5 mod 10 = 5

The expected check digit is 5, but the number ends in 7 — so this specific fake number fails the checksum. Paste it into the tool to see the breakdown live.

Every calculation runs locally. No data is uploaded or stored anywhere.