What a six-digit Korean stock code can and cannot tell you

Every stock listed in Korea carries a six-digit code, such as 005930 or 000660, assigned by Korea Exchange (KRX) and used much as a ticker is in the US. A company's name can change through a merger or rebranding, but its code generally stays the same. So those who handle data use the code rather than the name as the key. Jupick also stores its stock records by code and builds page addresses from the code.

Using codes as keys naturally leads to the next question: is other information hidden in those six digits? Stories circulate that the first digit shows the market, or that certain ranges belong to certain sectors. These are claims that can actually be checked, so Jupick checked them.

To start with the conclusion, the only thing that can be read from a code with certainty is the last character. The rest is mostly a sequence number. But that one last character matters quite a lot when building a list.

Some companies list more than one class of shares: common shares and preferred shares. These differ in voting rights and dividend terms and their prices move separately, but they share a single set of financial statements. The marker that tells them apart is in the last character of the code.

Common shares end in 0. Old-style preferred shares end in 5, 7 or 9. Samsung Electronics is 005930, and Samsung Electronics' preferred shares are 005935. When a company issues preferred shares more than once, the number goes up from 5 to 7 and then to 9.

New-style preferred shares issued since 1996 follow a different rule: the code ends in K or L. Mirae Asset Securities' second preferred B share is 00680K, and among preferred shares with letters there are codes such as 0220WL, with a letter in the second-to-last position as well. New-style preferred shares carry different terms from the old style, such as a set minimum dividend rate, so they use a separate notation.

As of August 29, 2026, a scan of all 2,767 stocks listed on KOSPI, Korea's main market, and KOSDAQ, Korea's second, growth-oriented market, finds 90 codes ending in 5, 7 or 9 and 24 codes ending in K or L. Together, 114 are preferred shares and the rest are common shares. If these 114 are not removed when building a list, the same company appears on two lines.

There is an easy point of confusion here. New-style preferred share codes contain letters, so it is tempting to conclude that any code with a letter is a preferred share. That conclusion is wrong.

KRX also assigns codes with letters to recently listed common shares. Samsung Epis Holdings has the code 0126Z0. There is a Z in the middle, but the last character is 0, and it is a common share. The letters are not a preferred share marker but a way to create more codes after the six-digit numeric combinations have been used up.

Among the 2,767 stocks, 56 codes contained a letter and ended in 0. Of these, 30 were special purpose acquisition companies (SPACs) with SPAC in their names, and the remaining 26 were common shares of ordinary operating companies. Conversely, all 24 codes that contained a letter and did not end in 0 were preferred shares.

In short, whether a code has a letter says nothing; only the last character does. A letter is at most a hint that the code was assigned recently.

For a long time, Jupick's Korean stock selection logic had two conditions: the code must end in 0, and all six characters must be digits. The second condition is exactly the premise shown to be wrong above. It filtered out codes with letters on the assumption that they were preferred shares.

Because of this condition, 26 common shares with letters in their codes were left out of the list regardless of market cap. Most ranked below the top 200 by market cap and would not have made the list anyway, but one was different. Samsung Epis Holdings has a market cap in the KRW 9 trillion range and ranks 75th overall. It belonged well inside a list of the top 200, yet it was quietly left out.

On August 29, 2026, this condition was removed. Now only whether the last character is 0 is checked. Preferred shares end in 5, 7, 9, K or L, so this one line filters them all out. The rule actually became shorter.

After the fix, the list was rebuilt, and among the 200 Korean stocks exactly one code contained a letter: Samsung Epis Holdings, 74th by market cap. With that one stock added, the stock that had been 200th was pushed out.

It is worth noting why this error went unnoticed for months. When data is wrong, something is usually blank or an odd value shows up. That was not the case here.

The list is sorted by market cap and then cut at the top 200. When the 75th stock is missing, the 76th fills its place, everything shifts up in a chain, and the stock that was originally 201st enters at the bottom. The count is still exactly 200.

Jupick has a safeguard that halts the whole day's update if the list comes in under 90% of its target. It exists to stop a wrong cleanup from running on a day when only half the listing data arrives, but since the count came to exactly 200, this safeguard did not react either. No number on screen was blank, and no warning went off.

Finding the missing stock meant looking not inside the list but outside it: taking the full set of listed stocks and checking, one by one, those caught by the filter. It is the kind of error that only appears when the question is not whether what is inside is right but why what is outside is outside.

There is a claim that the first digit of a code indicates the market. A check showed it does not. Common shares starting with 0 number 635 on KOSPI and 806 on KOSDAQ. Those starting with 1 number 71 on KOSPI and 276 on KOSDAQ, and those starting with 2 number 52 on KOSPI and 276 on KOSDAQ. Even the few codes starting with 9 are split across both, 2 on KOSPI and 20 on KOSDAQ.

No first digit belongs to only one market. When a KOSPI stock moves its listing to KOSDAQ, or the other way around, the code goes with it. The market has to be checked from a separate field, not from the code.

The same goes for sector. Codes are assigned roughly in listing order, so companies listed around the same time tend to have similar number ranges, and that is all; the same range does not mean the same sector. Size cannot be read either. Low numbers that belong to large companies, such as 000660, stand out and create that impression, but many companies with very small market caps also sit in the low ranges.

A code is enough for a rough guess at when a stock was listed. A code with a letter was almost certainly assigned recently. Going further than that is not safe.

Taking the lesson more broadly than the code rule itself, it comes to this. The rule that a code with a letter is a preferred share was actually true up to a certain point. In the days when new-style preferred shares used letters, those were the only codes that had them.

It became wrong not because the rule changed but because a new case appeared in the world. As numeric combinations ran out, letters began to appear in common share codes too, and a statement that used to be true became false from that day. The program kept running without a sound.

Rules of this kind are built by observing data, so when the data changes they quietly go stale. That is why what has been filtered out needs to be revisited now and then. Looking only at what passed, what passed always looks fine.

Other rules Jupick uses share the same nature. The rule that excludes names containing SPAC relies on the observation that SPACs are named that way, and the overseas list is a roster a person set once, so it does not follow changes in market cap rankings. Jupick considers it better to record what a rule relies on than to describe it as perfect.

The one thing that can be read with certainty from a six-digit Korean stock code is the last character. A 0 means a common share, 5, 7 or 9 an old-style preferred share, and K or L a new-style preferred share.

A letter in the code does not mean a preferred share. It is closer to meaning the code was assigned recently, and it also appears on common shares.

The first digit and the number range show neither the market, nor the sector, nor the size. That information has to be checked from separate fields, not from the code.

And whether something is missing from a list is hard to tell by looking at the list. Even when the count is right and every value is filled in, a stock may have been left out for the wrong reason. That actually happened at Jupick, and it is recorded above as it was.

This content is for information only and is not investment advice. Jupick does not encourage trading in any particular stock and does not forecast the future direction of stock prices, and the stocks used as examples serve only to explain the stock code system and are not an assessment or endorsement in any form. Investment decisions and responsibility for them rest with the user.