Fidelity counted 654,000 401(k) millionaires on its platform at the end of Q3 2025, out of 24.8 million participants. That works out to roughly 1 in 38 savers. The more interesting question is how long it took. The answer is buried in Fidelity’s long-term savings data, and once you run the math against the S&P 500’s actual return history, the timeline becomes obvious: this is a 30-year project on realistic assumptions.
What the continuous-saver data actually shows
Fidelity tracks workers who stay in the same plan with the same employer for extended periods. These are the cleanest case studies of what compounding actually does, because nobody cashed out, rolled over, or quit contributing. The average balance for 5-year continuous savers reached $304,200 at the end of 2025. Ten-year continuous savers averaged $459,000, and 15-year continuous savers averaged $613,200.
Notice what is happening between those lines. Five more years of saving and compounding added closer to $150,000, because the early years are mostly contributions, and the later years are mostly market growth. At 15 years in, the typical continuous saver still is not a millionaire. The gap from $613,200 to $1,000,000 is the entire back half of a career.
The math on a median income
Anchor this to a realistic paycheck. Median usual weekly earnings for full-time workers were $1,235 in Q1 2026, which, annualized, amounts to about $64,220. Fidelity’s framework assumes a 15% total savings rate, including the employer match. On that salary, that is roughly $9,633 per year, or $803 per month, going into the account.
Now apply a realistic return. The S&P 500, measured through SPY, returned 259% over the past 10 years and 451% from November 1999 through June 18, 2026. That long stretch annualizes to about 7% in price terms, closer to 9% including dividends. At an 8% annualized return, $803 a month compounds to roughly $1.13 million after 30 years. At 7%, it comes to about $910,000. The 30-year window is where the median earner crosses the line.
That projection assumes the median earner sticks to the plan. In practice, participant-wide data show that most savers fall short of these compounding curves long before year 30.
Why most savers are not on that path
The continuous saver data shows the ideal path. The full participant base tells a different story. The overall average 401(k) balance is $144,400, and balances by age peak only modestly: $199,900 for ages 50 to 54, $246,500 for ages 60 to 64, and $251,400 for ages 65 to 69. Those are averages, pulled higher by the millionaires at the top, while the typical 60-something is nowhere near seven figures, a gap that defines the reality behind retirement readiness and median versus average balances.
Three forces explain the gap, with contribution rates running below target. The average employee defers 9.5%, and the employer adds 4.7%, for a total of 14.2%, just under Fidelity’s 15% guideline. Leakage also matters: 37% of workers have taken an early or hardship withdrawal from a retirement account. And the national savings rate has compressed, falling from 6.2% in Q1 2024 to 3.7% in Q1 2026. Higher pay is not translating into higher savings.
The timeline, stated plainly
The 401(k) millionaire is almost always a 30-year story. Save 15% of a median income, leave it in a diversified equity-heavy portfolio, do not cash out between jobs, and historical S&P 500 returns put the median earner across the line in their late 50s or early 60s. Cut the savings rate to 8%, or start 10 years late, and the same math stalls out around $400,000 to $600,000, which is exactly where the continuous-saver averages sit today.
Two levers move the timeline the most. The 2026 contribution limit rose to $24,500 for workers under 50, with a $32,500 cap for ages 50-59. Using the catch-up after 50 is the cleanest way to accelerate the final decade. Staying invested through downturns is the other. The 15-year continuous savers who hit $613,200 stayed invested throughout.
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