The largest single-day percentage decline in S&P 500 history. Caused by portfolio insurance (systematic selling into a declining market) creating a feedback loop. The market fully recovered within 2 years and no recession followed.
ALAN INTELLIGENCE
ALAN INTELLIGENCE · alanglobalintelligence.com
ALAN IntelligenceData as of 2026-08-30
Bars: median S&P 500 forward return. Whiskers: 25th-75th percentile. n = 1 occurrences.
Based on 1 historical occurrences. Last triggered: 1987-10-19.
Past performance is not indicative of future results. This material is for informational and educational purposes only and does not constitute investment advice, an offer to buy or sell any security, or a recommendation. Data from publicly available sources believed to be reliable but not guaranteed. All investments involve risk, including possible loss of principal.
alanglobalintelligence.com
ALAN GLOBAL INTELLIGENCE · alanglobalintelligence.comSource: S&P 500 daily closes · Generated 2026-08-30
Historical occurrencesshowing 1 of 1
Date
1M return
1Y return
5Y return
1987-10-19
+8.1%
+22.9%
+81.2%
What history says
Editorial commentary written by ALAN analysts. Figures cited below are analyst-authored context — they are not derived from the chart above and may reflect different windows or sources.
The cleanest 'don't panic' case study in history
The economy never entered recession. Earnings continued growing. An investor who sold on October 20, 1987 permanently locked in a -22% loss for no fundamental reason.
This led to the creation of circuit breakers
After Black Monday, exchanges implemented trading halts (circuit breakers) to prevent mechanical selling cascades. These exist today at -7%, -13%, and -20% daily declines.
Full recovery: 2 years; forward 5-year return: +92%
An investor who held through Black Monday earned +92% over the next 5 years. An investor who sold and waited for 'clarity' missed most of that gain.
For your portfolio
Write down, in advance, what would actually change your allocation — a fundamental deterioration, not a price move. Black Monday's lesson is that a 22% one-day drop with no recession attached punished only those whose plan could be overridden by a single session's tape.
For information and research only. Not investment advice. ALAN does not place trades or execute orders. Figures come from the sources shown and can lag the market; verify independently before making decisions. Past performance is not predictive of future results.
LIVENYSE — · ETFEED MKT · — msBUILD ced8372
ALAN is not a broker-dealer or investment advisor. All data is informational only and does not constitute investment advice. Past performance does not guarantee future results.