S&P 500 Index Returns, Risks, and Warren Buffett’s Advice

There’s a reason the S&P 500 has become shorthand for “the stock market” itself: it tracks 500 of the largest US companies and has delivered steady growth over decades. Whether you’re a beginner wondering where to start or an experienced investor weighing your options, this guide lays out the index’s historical returns, what Warren Buffett really thinks, and the trade-offs of going all-in on U.S. large caps. By the end, you’ll have a clear picture of what the S&P 500 can—and can’t—do for your portfolio.

Current index value: 7,408.50 (as of May 15, 2026) ·
Number of companies: 500 leading US large-cap companies ·
Market coverage: Approximately 80% of total US stock market capitalization

The pattern is clear: longer holding periods smooth out volatility and amplify returns.

Four key facts that define the index today.

What exactly is the S&P 500 index?

How is it calculated?

• The index is market-cap weighted: each company’s weight is proportional to its total market capitalization (S&P Dow Jones Indices (official index provider)).
• Companies must meet specific criteria including market cap, liquidity, and sector representation.

What companies are included?

• The S&P 500 includes 500 of the largest publicly traded US companies, covering all major sectors (S&P Dow Jones Indices).
• As of May 2026, the index represents approximately 80% of US stock market capitalization (SEC (US regulator)).

The implication: The S&P 500 isn’t just any index — it’s the main lens through which US large-cap performance is viewed.

What is the 10 year return on the S&P 500?

What is the average annual return?

• Fidelity reports that the average 10-year return from January 2016 through December 2025 was 14.8% (Fidelity (investment broker)).
• Over the full 40 years ending December 2025, the average was 11.5% (Fidelity).
• Long-term 150-year annualized return (with dividends reinvested) is about 9.3% (Trade That Swing (market data aggregator)).

How does it compare to inflation?

• Inflation-adjusted 150-year average return is 6.9% (Trade That Swing).
• Over the past decade, the S&P 500 has significantly outpaced the average US inflation rate of roughly 3% per year (Bureau of Labor Statistics (US government)).

What this means: Real returns of 7–12% have historically beaten cash and bonds, but the gap narrows in high-inflation periods.

What if I invested $1000 in S&P 500 10 years ago?

What if I invested 20 years ago?

• A $1,000 investment in the S&P 500 10 years ago (assuming dividends reinvested) would now be worth approximately $3,200, based on a 10-year annualized return of 12.6% (Trade That Swing).
• Invested 20 years ago, using the 30-year average annual return of 10.4%, that $1,000 would be worth over $7,200 (Fidelity).

How does compounding work?

• Compounding multiplies returns over time as earnings generate further earnings. The S&P 500’s reinvestment of dividends accelerates growth.
• For context, the S&P 500’s historical dividend yield is about 1.3% (Sarwa (investment platform)), which added to price appreciation creates the total return.

The pattern: The longer the horizon, the more powerful compounding becomes — but it requires patience and discipline.

Can I become a millionaire by investing in the S&P 500?

Can you really become a millionaire with an S&P 500 ETF?

• Yes, consistent investing in a low-cost S&P 500 index fund over decades can build substantial wealth. For example, investing $500 per month for 30 years at an average 10% annual return would yield over $1 million (Fidelity (historical return data)).
• Warren Buffett has repeatedly recommended this approach as the best strategy for most investors (Berkshire Hathaway (2013 letter)).

How long would it take?

• Time horizon and contribution size matter. With $1,000 monthly contributions, you could reach $1 million in about 25 years at a 10% return. With $200 monthly, it would take over 40 years.

Why shouldn’t you just invest in the S&P 500?

What are the risks of investing only in S&P 500?

• The S&P 500 is US large-cap only and lacks exposure to international markets, small-cap stocks, and fixed income (SEC (diversification guidance)).
• Concentration risk: the top 10 stocks (e.g., Apple, Microsoft, Nvidia) make up a large percentage of the index, so a downturn in those companies can drag down the whole index.
• Historical returns are not guaranteed; the index can experience significant drawdowns (e.g., 2008 crisis, 2020 pandemic) (Fidelity (historical context)).

Why diversification matters

• A well-diversified portfolio including international stocks, bonds, and real estate can reduce overall volatility and provide more consistent returns.
• The SEC advises investors to diversify across asset classes to manage risk (SEC (investor bulletin)).

The trade-off: The S&P 500 is a great core holding, but going all-in exposes you to single-country risk and sector concentration.

Returns vary sharply by time horizon — one pattern is clear: longer periods smooth out volatility.

The implication: A single decade can mislead; only multi-decade data reveals the index’s true risk-adjusted return profile.

For the American retirement saver, the choice is clear: dollar-cost average into a low-cost S&P 500 fund, or accept the risk of missing out on long-term growth. The index isn’t a silver bullet — but combined with bonds and international exposure, it remains the most reliable engine for building wealth over decades.