Why the Market's Best Days Cluster Near Its Worst

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Missing 10 days over 20 years can halve your return — and they arrive during panics

01 The Concept

Market returns aren't spread evenly. A small handful of days produce a disproportionate share of long-run gains, and missing just a few of them devastates results — analyses commonly find that missing the ten best days over a couple of decades cuts final returns by roughly half. That alone would be an argument against trying to time the market.

The genuinely nasty part is when those days occur: the best days cluster tightly around the worst days, in the middle of crashes and panics. The biggest single-day gains in market history happened during the 2008 crisis and the 2020 crash — precisely when selling felt most obviously correct. So the investor who sells to avoid the crash reliably misses the rebound, because the rebound is inside the crash. This is why 'do nothing' outperforms most active behavior: staying invested through the worst days is the only way to be present for the best ones.

02 Case Study

CASEJ.P. Morgan Asset Management, *Guide to Retirement* annual analysis of S&P 500 best/worst days; Dalbar QAIB (Quantitative Analysis of Investor Behavior) annual study

J.P. Morgan's asset management arm publishes a recurring analysis of the S&P 500 that has become widely cited for one uncomfortable finding: over a typical 20-year window, an investor who stayed fully invested earned roughly double the return of one who missed just the ten best trading days — and missing the best 30 days could turn a solid positive return into a loss. The crucial detail is the clustering: a large majority of the best days occurred within two weeks of the worst days. Seven of the ten best days in one commonly cited window fell within two weeks of the ten worst. Meanwhile, Dalbar's annual QAIB study has for decades tracked the gap between fund returns and what actual investors earned in those same funds, consistently finding investors underperform their own holdings — because they buy after rises and sell after falls, systematically exiting right before the rebounds.

→ Why it matters

The market's best days sit inside its worst stretches, so avoiding crashes means missing recoveries. This is why Dalbar finds investors chronically underperform the very funds they own — the behavior, not the asset, is the problem.

03 Key Points

01A tiny number of days produce most long-run market gains

02Missing the ten best days over ~20 years can roughly halve final returns

03The best days cluster around the worst days — inside crashes and panics

04Selling to avoid a crash reliably means missing the rebound that lives inside it

Next: Ruin Risk: Why Averages Lie About Survival →