KOSPI weekly -0.93% (August 18–21) — 948 points moved, 65 points remained
The KOSPI ended the week at 6,912.95 on August 21, 2026, down 64.99 points or 0.93% from the August 14 close of 6,977.94. Between those two points the daily moves summed, in absolute terms, to 948.55 points. August 17 was a market holiday — the substitute day for Liberation Day, which fell on a Saturday
The three lines
- Week — 6,977.94 (Aug 14) to 6,912.95 (Aug 21), a net change of -64.99 points or -0.93%
- Range — daily moves summed to 948.55 points in absolute terms, 14.6 times the net change
- Circuit breakers — a sell-side sidecar on August 19 and a buy-side sidecar on August 20, on consecutive days in opposite directions
Key questions
- How much did the KOSPI move this week?
- By outcome, almost nothing. It closed at 6,977.94 on August 14 and 6,912.95 on August 21, down 64.99 points or 0.93%. Inside the week it looks different: -108.11 on August 18, -398.66 on August 19, +381.41 on August 20 and +60.37 on August 21. Ignore the signs and those sum to 948.55 points — 14.6 times the net change. For an investor watching only the index it was a quiet week. For anyone trading inside it, it was the roughest of the year.
- Why is there no report for August 17?
- The market was closed. Liberation Day, August 15, 2026, fell on a Saturday, so the following Monday, August 17, became a substitute public holiday and the Korean stock market closed with it. That leaves four trading days this week, Tuesday to Friday. It also means the reference point for the weekly comparison is not August 17 but the **August 14 close of 6,977.94**. This page set out how substitute holidays are designated in 'What a substitute holiday is', published the same day.
- What does it mean that sidecars fired on consecutive days?
- A sell-side sidecar triggered at 9:06:02 a.m. on August 19 and a buy-side sidecar at 9:57:10 a.m. on August 20 — the same mechanism twice, with only the direction reversed. A sidecar suspends the effect of program-trading orders for five minutes once a futures contract has moved beyond a threshold for one minute. One day it halted mechanical selling; the next it halted mechanical buying. That is what a market looks like when it crowds one way and then crowds back. A third sidecar fired on the KOSDAQ on August 21 — the fourteenth of the year — making three in a single week.
Read only the weekly return and the KOSPI fell 0.93% — a number that suggests nothing much happened.
948 points moved inside it.
1. Four sessions
Liberation Day 2026 fell on Saturday, August 15, so Monday, August 17 became a substitute holiday and the market closed. That leaves four trading days this week.
| Date | Close | Change | % |
|---|---|---|---|
| Fri Aug 14 (reference) | 6,977.94 | +164.60 | +2.42% |
| Mon Aug 17 | closed — substitute holiday | ||
| Tue Aug 18 | 6,869.83 | -108.11 | -1.55% |
| Wed Aug 19 | 6,471.17 | -398.66 | -5.80% |
| Thu Aug 20 | 6,852.58 | +381.41 | +5.89% |
| Fri Aug 21 | 6,912.95 | +60.37 | +0.88% |
| Week | -64.99 | -0.93% |
2. 948 against 65
The line that matters in that table is not the last one. It is the two in the middle.
| Measure | Value |
|---|---|
| Sum of absolute daily moves | 948.55 points |
| Net weekly change | -64.99 points |
| Ratio | 14.6× |
A 5.80% fall followed by a 5.89% rise leaves almost nothing in the weekly return. It leaves something in an account that lived through both days.
Measured with direction, the swing is wider still. The intraday high on August 18 was 7,216.62; the close on August 19 was 6,471.17. Within three sessions, 745.45 points — 10.3% from the high — disappeared and mostly returned. (The August 19 intraday low could not be confirmed, so the real range may be wider.)
3. Three sidecars in a week
| Date and time | Market | Direction | Trigger |
|---|---|---|---|
| Aug 19, 09:06:02 | KOSPI | sell-side | KOSPI 200 futures -6.02% |
| Aug 20, 09:57:10 | KOSPI | buy-side | KOSPI 200 futures +5.10% |
| Aug 21 (intraday) | KOSDAQ | sell-side | KOSDAQ 150 futures — the year's 14th |
A sidecar suspends the effect of program-trading orders for five minutes once index futures have moved past a threshold and stayed there for one minute. The KOSPI threshold is 5%; the KOSDAQ's is 6%.
Firing on consecutive days in opposite directions is the week in one line. One session needed mechanical selling stopped; the next needed mechanical buying stopped.
This page covered the mechanism on August 8 in "What a sidecar is — and how it differs from a circuit breaker" and on August 6 in "Sidecar trigger conditions: 5%, one minute, five minutes".
4. What moved it
Reporting through the week pointed to two forces.
US long rates. The US 30-year Treasury yield reached 5.337% intraday on August 17, its highest since 2007. When that yield rises, the stocks priced on distant future earnings are marked down first. Both the August 19 plunge and the KOSDAQ's 4.63% fall on August 21 were explained through this channel.
Two semiconductor names. SK hynix's board approved a 40 trillion won buyback and cancellation on August 19; the stock fell 9.75% that day and rose 12.73% the next. The market priced the filing a day late.
On August 21 that structure reached its extreme. 683 stocks fell on the main board while the index rose 0.88%, because Samsung Electronics (+3.87%) and SK hynix (+2.31%) outweighed everything else by market value.
5. The KOSDAQ went the other way
| Date | KOSPI | KOSDAQ |
|---|---|---|
| Aug 18 | 6,869.83 | 834.20 |
| Aug 19 | 6,471.17 (-5.80%) | 824.46 (-1.17%) |
| Aug 20 | 6,852.58 (+5.89%) | 840.89 (+1.99%) |
| Aug 21 | 6,912.95 (+0.88%) | 801.94 (-4.63%) |
On August 19 the KOSPI fell five times as far as the KOSDAQ; on August 21 the KOSPI rose while the KOSDAQ dropped 4.63%. The two markets moved together on only two of the four days.
The reason is composition. The KOSPI has semiconductor names large enough to carry the index alone. The KOSDAQ does not. It holds biotech, battery and robotics stocks, which are the most sensitive to long rates.
No weekly change is given for the KOSDAQ — the August 14 close could not be confirmed.
6. What is not confirmed
- The August 19 intraday low — not confirmed. The 745-point figure runs from an intraday high to a close, so the real range may be wider.
- Weekly flows by investor type — not confirmed. Even the daily figures diverged between outlets (foreign net selling on August 19 was reported at 4.02tn, 3.5tn and 2.9tn won), which makes simple addition unsafe.
- KOSDAQ weekly change — the August 14 reference close could not be confirmed.
- Next checkpoint — the Monday, August 24 open, and then the Jackson Hole keynote at 11:00 p.m. Korean time on August 28, which is widely named as the week's turning point. This page covered that event the same day in "Jackson Hole 2026".
Sources
- Ajunews — KOSPI closes at 6,977.94, up 164.60 points (2.42%) on August 14
- MBC News — KOSPI touches 7,200 intraday then closes in the 6,800s (August 18)
- Newspim — KOSPI plunges 5.80% to close at 6,471 on foreign and institutional selling (August 19)
- Hankyung — KOSPI falls more than 5% to the 6,400 level; sell-side sidecar triggered (August 19)
- Businesskorea — KOSPI recovers the 6,850 level amid a buy-side sidecar (August 20)
- Hankyung — KOSPI up 0.88% to 6,912.95; KOSDAQ closes down more than 4% (August 21)
- CBC News — Korea's 2026 Liberation Day substitute holiday falls on August 17