KOSPI rose on Friday while four in five of its stocks fell. Since late August, that is the rule, not the exception
The index gained 0.30% on 23 October as decliners beat advancers 716 to 173. Of 17 up days since late August, 9 had more fallers. The index is down 18.7% since 26 August; the median KOSPI stock, 6.9%.
AI-assisted, human-reviewed sourcing. Figures are pulled programmatically from the official sources listed at the end of this article and checked by an editor before publication.
kospimarket breadthsamsung electronicssk hynixkorea stocksadvancers decliners
The KOSPI closed 0.30% higher on Friday, 23 October, at 5,550.30. On the same day, according to Yonhap, 716 KOSPI stocks fell and 173 rose. Four in five stocks were down on a day the index was up.
That looks like an odd day. In the data we have collected since late August, it is closer to the normal pattern.
Up days when most stocks fell
We counted advancers and decliners on every KOSPI session from 27 August to 22 October, 37 trading days.
| Sessions | |
|---|---|
| Index rose | 17 |
| … and more stocks fell than rose | 9 |
| Index fell | 20 |
| … and more stocks rose than fell | 4 |
On more than half of the up days, most KOSPI stocks were down. The most lopsided before Friday was 16 September: the index rose 1.37% while 578 stocks fell and 304 rose. Friday’s 716 to 173 is wider than any up day in our window.
Two companies move the index
The reason is concentration. On 22 October, Samsung Electronics and SK hynix together made up 47.0% of the KOSPI’s market value. When both rise, the index can rise with most of the other 900-odd stocks falling. In August we found that four companies made up half of the market; the breadth count shows what that does day to day. On Friday, SK hynix rose 4.42% and Samsung 0.47%.
It works the other way too. On 28 September the index fell 2.70% while 611 stocks rose and 249 fell; Samsung lost 5.43% and SK hynix 5.05% that day.
The index fell further than the typical stock
| 26 August → 22 October | Change |
|---|---|
| KOSPI index | −18.7% |
| SK hynix | −27.5% |
| Samsung Electronics | −18.0% |
| Median KOSPI stock (940 listings) | −6.9% |
Most KOSPI stocks are lower than in late August: 721 of 940. But the typical one has fallen about a third as far as the index. The headline number since August is mostly a chip number.
What this does not say
Breadth counts each stock once, whether it is worth 1 trillion won or 1 billion. It says how many stocks moved each way, not how much money did. A wide gap between the index and the median stock tells you the index is carried by a few names; it does not tell you which way either goes next.
Korea Exchange daily KOSPI stock and index data, 27 August – 22 October 2026, collected daily by SeoulMarkets; 23 October close and breadth from Yonhap. Not investment advice.
Data & Verification Notes
- Data as of
- Sources
- Korea Exchange (KRX OPEN API) — KOSPI daily stock trading (closing price, change, market capitalisation for every KOSPI listing) and KOSPI index daily close, 37 trading days from 27 August to 22 October 2026, collected daily by SeoulMarkets.
- Yonhap News Agency (via Korea JoongAng Daily and press reports) — 23 October 2026 close: KOSPI 5,550.30 (+16.53, +0.30%); decliners 716, advancers 173; Samsung Electronics +0.47% to 215,500 won; SK hynix +4.42% to 1.28 million won.
- Cross-checks
- Our 22 October KOSPI close, 5,533.77, plus Yonhap's +16.53 points gives 5,550.30, the reported 23 October close.
- Up days with more decliners than advancers (advancers/decliners), 27 Aug–22 Oct: 27 Aug 317/539; 31 Aug 366/489; 3 Sep 424/433; 16 Sep 304/578; 18 Sep 407/464; 21 Sep 310/552; 22 Sep 383/463; 23 Sep 311/546; 21 Oct 372/490.
- Down days with more advancers than decliners: 28 Aug 640/238; 17 Sep 453/398; 28 Sep 611/249; 14 Oct 503/371.
- KOSPI index: implied 26 August close 6,808.20; 22 October 5,533.77; change −18.7%. Median change of 940 KOSPI listings over the same period −6.9%; 721 are lower.
- Samsung Electronics (common) −18.0% and SK hynix −27.5% over 26 Aug–22 Oct. Counting common shares only (Samsung's preferred shares excluded), the two hold 47.0% of KOSPI market capitalisation on 22 October.
- Excluded figures
- 23 October stock-by-stock data: our daily file for that session was not yet in when we wrote. The 23 October breadth figures are Yonhap's, not our count.
- KOSDAQ. This piece is KOSPI only.
- Stocks with no trade on a given day are left out of that day's advancers and decliners; unchanged stocks count as neither.
- This is not investment advice.
- Instruments
- 005930, 000660
The full dataset behind these figures — every listed company, every row — is available to license. SeoulMarkets data for licence →
Not investment advice. SMarkets publishes data journalism for general information only. Nothing here is investment advice, a recommendation, or an offer to buy or sell any security — any investment you make is at your own risk and responsibility. Figures are derived from official public data sources and may be revised by the issuing agency. Verify independently before acting.
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