KOSPI Plunges 7.57% After CPI: Why Was It the Worst in 23 Releases?
KOSPI fell 7.57% the day after the CPI release.
A drop this big after CPI hasn't happened in the past two years.
The US September CPI came out on October 14 at 21:30 Korean time.
Domestic stocks had their first reaction on October 15.
Retail investors: "A single price number wipes out 7%?"
The number alone only tells half the story.
Let's break it down.
The Numbers First
KOSPI: 5,554.22 (-7.57%)
KOSDAQ: 760.82 (-7.65%)
Largest previous next-session drop after CPI: -3.26% (2026-09-14)
This is the biggest decline in 23 releases since October 2024.
It's more than double the old record!!!
The next CPI lands on November 10 at 22:30 Korean time.
What CPI Actually Measures
CPI is the price report card for what consumers pay for goods and services.
The US Bureau of Labor Statistics (BLS) publishes it every month.
The market uses it to gauge the direction of interest rates.
Why a Hot CPI Shakes Stocks
When inflation runs hot, rate cuts get harder.
Higher rates for longer shrink the present value of future earnings.
The discount rate is the rate used to convert future profits into today's value. (Rates and stocks move like a seesaw)
That's why growth stocks, which depend on distant expectations, react first.
Recent US sector performance fit that pattern exactly.
IT and semiconductors: -2.98%
Healthcare: +2.53%
Consumer staples: +2.22%
On October 15, headlines tied the semiconductor selloff to inflation data.
Breaking news also reported that Hanmi Semiconductor plunged in the 8% range as Samsung Electronics and SK hynix weakened.
With semiconductors weighing heavily on KOSPI, the CPI shock spreads quickly.
Was CPI the Only Reason KOSPI Crashed?
This is a common misconception.
KOSPI was already sliding before CPI.
10/12: -3.65%
10/13: -5.46%
10/14: -0.44%
From October 6 to 15, it fell seven straight trading days.
From 7,003.74 on October 2 to 5,554.22 on the 15th, the cumulative drop is -20.70%.
Headlines also pointed to oil prices and US inflation together.
CPI landed as a final blow on a market already spooked...
Does KOSPI Always Fall the Day After CPI?
That's a misconception too.
Average over the last 23 releases: +0.97%
16 rises, 7 declines.
Largest gain: +6.24% (2026-07-15)
Even recently, the direction has varied: 5/13 +2.63%, 8/13 +3.56%, 9/14 -3.26%.
The better way to think about CPI's market impact is the size of the swing, not the direction.
Whether the number came in hotter or cooler than expected decides the direction.
When Is the Next CPI Release?
US October CPI: November 10 at 22:30 (Korean time)
US November CPI: December 10 at 22:30 (Korean time)
It's one hour later than this time because US daylight saving time ends.
Domestic reaction comes from the market open the following day.
The December 10 release falls the day after the FOMC, so rate decisions and inflation data arrive back to back.
You can check all the dates in one place on the market calendar.
So, What Should You Remember?
On CPI days, I look at the week leading up to it before the number itself.
- Remember that CPI lands at night Korean time, and KOSPI reacts the next day.
- Don't explain a crash with CPI alone, check the moves in the days before the release too.
- Before the next CPI, note the US 10-year yield at 5.089%, WTI at $95.82, and the exchange rate at 1,342.53 won.
Release schedules can change, so check the BLS notice or your brokerage calendar for the latest dates.
Just keep this as a reference!
PickStock 💡
※ Investment decisions and responsibility rest with the investor.
※ Figures are as of the time of writing and may change.
※ This article is for information only and is not investment advice.
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