KOSPI weekly −1.50% (August 31 – September 4, 2026) — four up days lost to one down day
The KOSPI closed the week of August 31 to September 4, 2026 at 6,687.21, down 101.67 points or 1.50 percent from the prior Friday close of 6,788.88. The shape behind that number is unusual. Four of the five sessions were higher — August 31 up 0.46 percent to 6,820.02, September 1 up 0.23 percent to 6,835.80, September 3 up 0.26 percent to 6,579.48 and September 4 up 1.64 percent to 6,687.21 — and only one was lower. But September 2 fell 273.08 points, or 3.99 percent, and the four gains together came to just 171.41 points. The week's high close and low close, 6,835.80 and 6,562.72, fell on consecutive days, so roughly 4 percent of the index moved within a single 24-hour span. The causes came from outside Korea: oil above 95 dollars a barrel on renewed US-Iran fighting, the US 10-year yield at its highest since January 2025, and corporate buybacks adding more than a trillion won of demand every session
The three lines
- Week — 6,788.88 to 6,687.21. Down 101.67 points, 1.50 percent, with four up days and one down day
- The one day — September 2 fell 273.08 points (3.99%), more than the 171.41 points gained across the other four
- Drivers — Brent above $95, the US 10-year yield at 4.79%, and buybacks putting a floor under each session
Key questions
- How far did the KOSPI fall this week
- **101.67 points, or 1.50 percent**, from **6,788.88** on August 28 to **6,687.21** on September 4. Session by session: August 31 **6,820.02** (+31.14, +0.46%), September 1 **6,835.80** (+15.78, +0.23%), September 2 **6,562.72** (−273.08, −3.99%), September 3 **6,579.48** (+16.76, +0.26%), September 4 **6,687.21** (+107.73, +1.64%). **Four sessions higher, one lower, and a negative week.** The four gains total 171.41 points; the single loss was 273.08. The gap between the highest close (September 1) and the lowest (September 2) is also exactly 273.08 points, and those two closes were **consecutive sessions** — about 4 percent of the index inside a day. The KOSDAQ finished the week at **813.50** on September 4, up 2.95 percent, retaking the 800 level it had lost the previous session.
- What happened on September 2
- **Two external inputs arrived on the same day.** The first was **oil.** On September 1 the United States launched fresh strikes on Iranian targets, and Brent crude moved above **95 dollars a barrel**, which markets read as an inflation problem. The second was **rates.** The same day the US 10-year Treasury yield reached **4.79 percent**, its highest since January 2025. Because the Federal Reserve is currently weighing a rate rise rather than a cut, that combination transmits directly into equities. Inside Korea, **foreign investors and institutions sold a combined 4 trillion won**, and Samsung Electronics and SK hynix each fell about 4 percent, pulling the index down with them. One detail is worth keeping: on that fall, **individual investors bought a net 2.30 trillion won**, absorbing the supply — and then spent the following two sessions selling it back, culminating in 3.72 trillion won of retail selling on September 4.
- Which way does next week go
- **The premise behind Friday's gain collapsed on Friday night.** The KOSPI rose 1.64 percent on September 4 on the back of a strong US session, and that US strength came from September rate-rise odds falling after remarks by Fed governor Christopher Waller. Then, at **21:30 Korean time on September 4**, the US August payrolls report landed: **162,000 new jobs**, roughly triple the forecast, with July revised from −23,000 to +21,000. Odds of a hike went back up and the S&P 500 closed 0.38 percent lower. **The premise and the fact point opposite ways.** At least three inputs are now competing for the next session: **rates** (the September 15–16 FOMC), **oil** (on September 5 US Central Command said it struck three Iranian oil tankers), and **semiconductors** (August chip exports set a monthly record of 46.65 billion dollars, while US chip tariffs remain unresolved). Which dominates is not established.
The week finished at −1.50 percent, and four of the five sessions were up.
Between August 31 and September 4 the KOSPI went from 6,788.88 to 6,687.21, a loss of 101.67 points. Read as a number it looks like a mild down week. Read session by session it looks nothing like one.
1. One day swallowed four
| Date | Close | Change | Percent |
|---|---|---|---|
| August 28 (prior Friday) | 6,788.88 | — | baseline |
| August 31 (Mon) | 6,820.02 | +31.14 | +0.46% |
| September 1 (Tue) | 6,835.80 | +15.78 | +0.23% |
| September 2 (Wed) | 6,562.72 | −273.08 | −3.99% |
| September 3 (Thu) | 6,579.48 | +16.76 | +0.26% |
| September 4 (Fri) | 6,687.21 | +107.73 | +1.64% |
| Week | 6,687.21 | −101.67 | −1.50% |
The four gains add up to 171.41 points. The single loss was 273.08.
The distance between the week's highest close (September 1) and lowest close (September 2) is the same 273.08 points — and those were consecutive sessions. About 4 percent of the index turned over inside 24 hours.
2. What made that day
Nothing in the September 2 move originated in Korea.
Oil. US strikes on Iranian targets on September 1 pushed Brent above 95 dollars a barrel. Oil feeds inflation and inflation feeds rates.
Rates. The same day the US 10-year Treasury yield hit 4.79 percent, the highest since January 2025. With the Fed weighing a rise rather than a cut, that lands straight on equity valuations.
Domestically, foreign investors and institutions sold a combined 4 trillion won, and Samsung Electronics and SK hynix each dropped around 4 percent.
3. A trillion won arrived every day regardless
Part of the reason the index recovered in two sessions was a bid that had nothing to do with sentiment.
Net buying by "other corporations" — the category that captures company share repurchases — ran at 1.65 trillion won on September 2, 1.61 trillion on September 3 and 1.57 trillion on September 4, three consecutive sessions above 1.5 trillion. Samsung Electronics is running a 15 trillion won buyback to November 21 and SK hynix a 40 trillion won programme to November 19.
This is the arithmetic behind September 4. Retail investors sold 3.72 trillion won and the index still rose 1.64 percent, because institutions (1.67tn), other corporations (1.57tn) and foreigners (about 0.5tn) together came within 24 billion won of matching them.
That bid has an expiry date — November 21 and November 19 respectively.
4. What is still open
- Friday's premise was undone on Friday night. The rally rested on falling September hike odds; the US August payrolls report released at 21:30 Korean time on September 4 (162,000 jobs, roughly triple the forecast) reversed that.
- Oil moved further over the weekend. On September 5 US Central Command said it struck three Iranian oil tankers. Brent settled at 96.28 dollars on September 4, up close to 9 percent on the week.
- Semiconductors point both ways. August chip exports were a record 46.65 billion dollars, while US semiconductor tariffs remain under negotiation.
- The weekly figure here is calculated, not official. It uses the August 28 and September 4 closes and was not checked against a Korea Exchange weekly tally, and intraday extremes were not examined.
Sources
- Asiae — KOSPI closes at 6835.80, up 15.78 points (+0.23%)
- MoneyToday — KOSPI closes up 15.78 points (0.23%) at 6835.80
- Businesskorea — Market close: KOSPI edges up to 6,835.80 in mixed trade
- Asiae — KOSPI closes at 6687.21, up 107.73 points (+1.64%)
- MoneyToday — KOSPI closes up 107.73 points (1.64%) at 6687.21
- Yahoo Finance — Stock market today: Dow, S&P 500, Nasdaq drop as oil tops $95, bond yields rise (September 1)