Warren Buffett has a standing bet: over any 10-year period, a low-cost S&P 500 index fund will outperform a hand-picked basket of hedge funds. He has won every time. That is the power of index fund investing — and in 2026, it is more accessible than ever to start with as little as $100.
Index funds are the single most effective wealth-building tool available to ordinary people. They require no stock-picking skill, no market timing, and no financial advisor. You buy a slice of the entire market and then do nothing — year after year — while the power of compounding and economic growth does the heavy lifting.
In this guide, you will learn exactly how index funds work, which ones to buy in 2026, and how to start with just $100.
Key Takeaway
$100 invested monthly in an S&P 500 index fund averaging 10% annual returns grows to $20,000 in 10 years, $75,000 in 20 years, and $230,000 in 30 years. Starting early and staying consistent matters far more than picking the "perfect" fund or timing the market.
What Is an Index Fund?
An index fund is a type of mutual fund or ETF that tracks a specific market index — most commonly the S&P 500, which holds the 500 largest publicly traded U.S. companies. When you buy an S&P 500 index fund, you are buying a tiny piece of Apple, Microsoft, Amazon, Nvidia, Google, Meta, Berkshire Hathaway, and 493 other companies in proportion to their market value.
The key features that make index funds powerful:
- Diversification: One fund gives you exposure to hundreds or thousands of stocks. If one company collapses, it barely affects your portfolio.
- Rock-bottom fees: The best index funds charge expense ratios of 0.015% to 0.09%. For every $10,000 you invest, you pay $1.50 to $9.00 per year in fees. Actively managed mutual funds charge 10-20x more.
- Tax efficiency: Index funds trade infrequently, which means fewer taxable capital gains distributions than actively managed funds.
- Simplicity: You do not need to research stocks, read earnings reports, or follow financial news. Buy the fund and hold it indefinitely.
The difference between a 0.03% expense ratio (VOO) and a typical 1.2% actively managed fund does not sound large — but over 30 years on a $100,000 portfolio, it amounts to roughly $300,000 in lost returns. Fees are the single factor you can control, and index funds minimize them.
Why Index Funds Beat Active Management
The data is overwhelming. Over the 20 years ending in 2025, approximately 85% of large-cap U.S. stock fund managers underperformed the S&P 500, according to the SPIVA Scorecard from S&P Global. Over 10 years, trailing stretches to 90%. Even the few managers who beat the market in one decade rarely repeat it in the next.
This is not a coincidence. Active managers face structural disadvantages: they must pay analysts, traders, and compliance teams; they incur trading costs every time they buy or sell; they are subject to behavioral biases like herding and loss aversion; and they face the constant pressure of quarterly performance reviews that encourage short-term thinking.
Index funds eliminate all of these disadvantages. They do not try to beat the market — they are the market. And over time, the market tends to go up. Since 1926, the S&P 500 has delivered an average annual return of approximately 10% before inflation. There have been bear markets, crashes, and lost decades, but every single 20-year period in U.S. stock market history has produced a positive return.
"Don't look for the needle in the haystack. Just buy the haystack." — John Bogle, founder of Vanguard
Best Index Funds to Buy in 2026
In 2026, the best index funds continue to be the ones with the lowest fees, most diversification, and longest track records. Here are the top picks:
| Fund | Index | Expense Ratio | Minimum | Best For |
|---|---|---|---|---|
| VOO (Vanguard S&P 500 ETF) | S&P 500 | 0.03% | 1 share (~$480) | Core US large cap |
| VTI (Vanguard Total Stock Market) | CRSP US Total Market | 0.03% | 1 share (~$260) | Total US market exposure |
| VT (Vanguard Total World Stock) | FTSE Global All Cap | 0.07% | 1 share (~$115) | One-fund global portfolio |
| FXAIX (Fidelity 500 Index) | S&P 500 | 0.015% | $0 | Lowest fee, no minimum |
| FSKAX (Fidelity Total Market) | Dow Jones U.S. TSM | 0.015% | $0 | Fidelity users, lowest fee |
| SWTSX (Schwab Total Stock Market) | Dow Jones U.S. TSM | 0.03% | $0 | Schwab users |
| QQQM (Invesco NASDAQ 100) | NASDAQ-100 | 0.15% | 1 share (~$195) | Tech-heavy exposure |
How to Start with $100
Many brokerages now allow you to buy fractional shares of ETFs, meaning you can start with any dollar amount — even $10. Here is the exact 5-step plan to begin with $100:
Step 1: Open a brokerage account (20 minutes). Fidelity, Charles Schwab, and Vanguard are the Big Three. Fidelity and Schwab have no account minimums. Vanguard requires $1,000 for mutual funds but has no minimum for ETFs. All three offer fractional ETF shares.
Step 2: Fund the account. Link your bank account. Transfer your $100 (or any amount). The transfer takes 1-3 business days to settle.
Step 3: Choose your first fund. For a $100 start, the simplest option is VT (Vanguard Total World Stock ETF) at ~$115/share — you would buy 0.87 fractional shares. Alternatively, for US-only exposure, buy VTI (Vanguard Total Stock Market ETF) at ~$260/share — you would buy 0.38 fractional shares. On Fidelity, buy FXAIX with a direct $100 (no fractional ETF needed, no minimum).
Step 4: Set up automatic investments. The real magic happens when you automate. Set up a recurring transfer of $50, $100, or whatever you can afford on the same day each month. Fidelity's automatic investing works with fractional shares of ETFs. Schwab and Vanguard offer automatic mutual fund investing.
Step 5: Do not touch it. This is the hardest step. Market drops will happen — the S&P 500 has fallen at least 10% in 11 of the last 20 years. Every drop is a buying opportunity. Keep investing on schedule regardless of what the market does. Over 30 years, what matters most is time in the market, not timing the market.
Choosing a Brokerage Account
| Broker | Min Deposit | Fractional Shares | Best Feature |
|---|---|---|---|
| Fidelity | $0 | Yes (ETFs) | Lowest fees (0.015%), great App |
| Charles Schwab | $0 | Yes (S&P 500 stocks) | Excellent research tools |
| Vanguard | $0 (ETFs) | Yes (ETFs) | Founder of index investing |
| Robinhood | $0 | Yes | Simplest UI, instant deposits |
| M1 Finance | $0 | Yes (pies) | Auto-rebalancing pies |
| Betterment | $0 | Yes (robo) | Fully automated management |
Beginners' Mistakes to Avoid
Mistake #1: Trying to time the market. In 2020, the S&P 500 fell 34% in 33 days and then doubled in 18 months. Investors who sold at the bottom missed the fastest recovery in history. You cannot predict short-term market movements. Do not try.
Mistake #2: Checking your portfolio too often. The stock market goes up and down every day. If you check your balance daily, you will feel anxious about normal volatility. Check quarterly or annually at most.
Mistake #3: Buying too many funds. You do not need 10 different index funds. Two — a US total market fund and an international fund, or just one global fund (VT) — is enough. More funds create overlap and complexity without additional diversification.
Mistake #4: Investing before paying off high-interest debt. If you have credit card debt at 24% APR, paying that down should come before investing. No investment reliably returns 24%. The exception is low-interest debt like mortgages and student loans.
Mistake #5: Selling during a crash. Every bear market in history has been followed by a bull market that exceeded the previous peak. Selling during a crash turns a temporary loss into a permanent one. Stay invested.
Your Action Plan
Open a Fidelity or Schwab account this week. Fund it with $100. Buy FXAIX (Fidelity) or VTI (Schwab or Vanguard). Set up a recurring monthly investment of whatever you can afford — even $25/month compounds to meaningful wealth over time. Then do not touch it for 10 years. The hardest part is starting, and you now know exactly how to do it.