What Happens If You Miss the 10 Best Days

J.P. Morgan Asset Management publishes one of the most cited studies in all of investment research. They tracked a $10,000 investment in the S&P 500 over 20 years from 2003 to 2023. An investor who stayed fully invested the entire time ended up with about $64,844. An investor who missed the 10 best days ended up with $29,708 — less than half. Miss the 20 best days: $17,826. Miss the 30 best days: $11,701. Miss the 40 best days: $7,594. At that point, you would have been better off in a savings account. The stock market's entire excess return over safer investments is concentrated in a tiny number of explosive up days. Miss them, and you're not investing — you're just taking risk for nothing.

Why the Best Days Matter So Much

The distribution of stock market returns is wildly uneven. Most trading days produce small, forgettable moves. The real returns come from a handful of massive up days that are nearly impossible to predict. These extreme positive days tend to follow extreme negative days — the snapback rallies after panics, the relief rallies after crises.

Here's the pattern in the data: six of the 10 best days in the 20-year period from 2003-2023 occurred within two weeks of the 10 worst days. The single best day was March 24, 2020 — a 9.4% spike that occurred the day after the COVID crash bottom. If you sold during the panic to "protect yourself," you almost certainly missed the very best day. This isn't a coincidence. It's a structural feature of how markets work. Panic selling exhausts itself, and the subsequent buying wave creates enormous single-day returns.

The math of missing big days is asymmetric and unforgiving. If you're invested for the 10 worst days but also the 10 best days, the net effect is minimal — the good days roughly offset the bad. But if you avoid the worst days and also miss the best days, you've eliminated the engine of long-term returns without meaningfully reducing risk. The worst days are the price of admission for the best days. You can't have one without the other.

This data point is one of the strongest arguments against market timing. To successfully avoid the 10 worst days, you'd need to sell before the crash (almost impossible to time) and buy back in before the recovery (equally impossible to time). The probability of correctly executing both sides of this trade, even once, is extremely low. Doing it consistently across multiple cycles is essentially impossible.

Why It Matters for Investors

The "missing the best days" data reinforces a simple truth: your biggest risk in the stock market isn't a crash — it's not being invested during the recovery. Crashes are temporary. The S&P 500 has recovered from every single downturn in its history. But if you sell during the crash and miss the first days of the recovery, those losses become permanent because you've given up the best days that drive long-term returns.

This data should inform your investment strategy directly. Automatic contributions — investing the same amount every month regardless of market conditions — ensure you're always invested and always positioned to capture the best days. Sitting in cash "waiting for a pullback" means you might miss one of those explosive up days that drives years of returns.

The argument also applies to asset allocation. Investors who shift from stocks to bonds or cash during uncertainty are, by definition, removing themselves from the market where the best days occur. Even if they avoid some of the worst days, they systematically miss the best days — and the data shows that missing the best is far more costly than avoiding the worst.

Real Example

An investor had $200,000 in the S&P 500 in early 2020. On March 12, the market fell 9.5% — one of the worst days in history. Panicked, they sold everything on March 16. Over the next three days, the market fell another 12%, so at first they felt vindicated. But then on March 24, the market surged 9.4% (the best day in 12 years). On March 26, it jumped another 6.2%. By early April, the market had recovered 25% from the bottom. Our investor was still in cash, waiting for "confirmation" that the recovery was real. By the time they reinvested in June, they had missed a 40% rally from the bottom. Their $200,000 became roughly $150,000 after the sale and sat in cash while a fully invested portfolio would have been back to $200,000 and climbing. They avoided the last few days of the decline but missed the best days of the recovery — and the recovery was worth far more than the decline they avoided.