Why Missing Just 10 Days in 20 Years Can Cut Your Stock Market Returns in Half

TL;DR JPMorgan's study of the S&P 500 from 2003 to 2023 showed that missing just the 10 best trading days cut annualized returns nearly in half (from 9.8% to 5.6%), and missing 30 days meant losing money entirely. Seven of the 10 best days occurred within two weeks of the worst days, which is why panic selling systematically destroys wealth.

March 2020: When Fear Took Over

I remember it vividly. COVID-19 was sweeping across the globe, and the S&P 500 cratered over 30% in a single month. Investors around me were liquidating portfolios in a frenzy. The logic felt airtight at the time: get out before it gets worse.

What happened next was one of the fastest market recoveries in history. Those who panic-sold missed almost all of it. Those who held saw their portfolios recover within months.

The JPMorgan Data That Changes Everything

JPMorgan analyzed S&P 500 returns over a 20-year period from 2003 to 2023. The findings are hard to forget once you see them.

Scenario	Annualized Return
Fully invested for 20 years	9.8%
Missed the 10 best days	5.6%
Missed the 20 best days	2.9%
Missed the 30 best days	Negative

Out of roughly 5,040 trading days across two decades, missing just 10 of them nearly halved your returns. Missing 30 — that's 0.6% of all trading days — and you actually lost money.

When I present this data to my students, the room goes quiet. A single table conveys what hours of theoretical explanation cannot.

The Best Days Hide Right Next to the Worst

Here's the detail that makes market timing structurally doomed.

Seven of the 10 best trading days occurred within two weeks of the worst days.

Think about what this means in practice. The market drops 30%. You're terrified. You sell. Now you're sitting in cash, waiting for it to drop further before you buy back in. But historically, the biggest rebounds happen almost immediately after the biggest crashes. By the time you feel safe enough to re-enter, the recovery has already happened.

In theory, buying at the bottom and selling at the top is the optimal strategy. In practice, nobody executes it. Not retail investors, and not most professionals either. The emotional toll of a crash makes rational timing virtually impossible. During COVID, people who sold weren't thinking "I'll get back in within two weeks." They were waiting for months, expecting further drops that never came.

Keep Short-Term Money Out of the Market

Instead of trying to time entries and exits, a better framework has two parts.

First, money you'll need within three years doesn't belong in the stock market at all. House down payments, upcoming major repairs, near-term large expenses — these should sit in high-yield savings accounts, CDs, or short-term treasuries like T-bills or the SGOV ETF. Returns will be modest at 3.5% to 4.5%, but you won't lose 20% overnight when the market corrects.

The S&P 500 has delivered negative five-year returns about 12% of the time historically. In any given year, a 10% or greater drawdown occurs roughly one out of every three years. Exposing short-term money to that risk is gambling, not investing.

Second, long-term investment capital should go in through dollar-cost averaging. Automate a fixed amount each month. Stop watching daily price movements. The evidence overwhelmingly shows that consistent, emotionless investing outperforms active timing for the vast majority of people.

The Uncomfortable Truth

The hardest part of this rule isn't understanding it. It's sitting still when every fiber of your being screams at you to do something. Crashes feel like emergencies. Your brain treats portfolio losses the same way it treats physical threats. But the data is unambiguous: the investors who do nothing during crashes systematically outperform those who act on their fear.