Index Fund Investing: The Only Strategy You Need to Build Wealth

Index fund investing is the strategy that has made more ordinary people wealthy than any other approach in the history of financial markets. It’s not glamorous. It doesn’t require a Bloomberg terminal or a finance degree. But over any 20-year period in the S&P 500’s history, index fund investing has beaten the vast majority of professional money managers. That’s not an opinion. It’s documented fact.

Index fund investing is what Warren Buffett recommended for most people when he wrote his will. He instructed his trustee to put 90% of the cash he leaves behind into an S&P 500 index fund. If it’s good enough for the world’s greatest investor to recommend for his own heirs, it’s worth understanding exactly how it works.

This post covers everything: what index funds are, why they beat active management, expense ratios, the best funds for beginners, how to buy them, and realistic return expectations with real numbers over 20-30 years.

What Is Index Fund Investing?

An index fund is a type of investment fund that tracks a specific market index. The most common is the S&P 500, which holds the 500 largest publicly traded U.S. companies. When you buy an S&P 500 index fund, you’re buying a tiny piece of all 500 companies at once.

Index fund investing is passive investing. Nobody is sitting in a room deciding which stocks to buy and sell. The fund just mirrors whatever is in the index. Apple goes up, your fund goes up. The whole market drops, your fund drops too. You own the whole market, which means you capture the whole market’s returns.

This sounds simple, but it’s the simplicity that makes it powerful. The fund doesn’t need armies of analysts. It doesn’t pay traders to try to outsmart the market. Those savings get passed directly to you in the form of extremely low fees.

Why Index Fund Investing Beats 90% of Active Managers

The SPIVA report from S&P Global tracks active fund performance against index benchmarks every year. The results are consistent: over any 15-year period, roughly 85-92% of actively managed funds underperform their benchmark index after fees.

Why? Three reasons:

1. Fees Kill Returns

The average actively managed mutual fund charges about 0.6% to 1.0% per year in expenses. An index fund might charge 0.03% to 0.10%. That difference seems tiny. But on a $100,000 portfolio over 30 years at 8% returns, a 1% fee difference costs you roughly $130,000 in lost wealth. Fees compound just like returns do, except they work against you.

2. Market Timing Is Nearly Impossible

To beat an index fund through active management, you need to consistently pick the right stocks AND buy and sell at the right times. J.P. Morgan Asset Management has published research showing that six of the best ten trading days in the stock market each decade happen within two weeks of the ten worst days. If you’re on the sidelines during a drop, you’ll likely miss the recovery too.

3. Tax Inefficiency

Active funds trade frequently. Each trade can generate a taxable event. Index funds rarely trade because the underlying index rarely changes. That makes index fund investing far more tax-efficient in a taxable account.

Expense Ratios: The Number That Matters Most in Index Fund Investing

The expense ratio is the annual fee an index fund charges, expressed as a percentage of your investment. A 0.03% expense ratio on a $10,000 investment costs you $3 per year. A 1.0% expense ratio on the same investment costs $100.

Here’s how expense ratios compound over time on a $50,000 portfolio growing at 8% annually:

That’s $89,000 lost to fees over 30 years. On a $50,000 starting investment. When talking about index fund investing, the expense ratio is everything.

The 3 Best Index Funds for Beginners

You don’t need 20 funds. You don’t need to pick sectors or themes. Here are the three index funds that form the core of most simple, powerful portfolios:

VTI: Total U.S. Stock Market

VTI (Vanguard Total Stock Market ETF) holds more than 3,600 U.S. stocks across large, mid, and small-cap companies. It’s the broadest exposure to the U.S. economy you can get in a single fund.

• Expense ratio: 0.03%
• 10-year average annual return (through 2025): roughly 13%
• Best for: core equity holding in any portfolio

VOO: S&P 500 Index

VOO (Vanguard S&P 500 ETF) tracks the 500 largest U.S. companies. It’s slightly more concentrated than VTI (fewer small-cap stocks) but has historically performed nearly identically. This is what most people mean when they say “just buy the S&P 500.”

• Expense ratio: 0.03%
• 10-year average annual return (through 2025): roughly 13.5%
• Best for: investors who want the most widely tracked index

SCHD: Dividend-Focused Index

SCHD (Schwab U.S. Dividend Equity ETF) tracks high-quality dividend-paying U.S. stocks. It’s not purely a growth index fund, but it provides income plus appreciation with excellent historical performance.

• Expense ratio: 0.06%
• Dividend yield: approximately 3.5-4%
• Best for: investors who want income plus growth, especially for taxable accounts or retirement portfolios

A simple two or three fund portfolio using VTI (or VOO) plus SCHD covers most investor needs. A full breakdown of these ETFs and more options is available in the best ETFs guide.

ETFs vs Mutual Fund Index Funds: What’s the Difference?

Both ETFs and mutual fund index funds can track the same index, but they work slightly differently:

For most beginners, ETFs are the easier starting point. You can buy VTI with as little as one share and start index fund investing the same day you open an account. VTSAX is nearly identical to VTI but requires a $3,000 minimum to start at Vanguard.

How to Buy Index Funds: Step by Step

Getting started with index fund investing takes about 20 minutes. Here’s the exact process:

1. Open a brokerage account. For retirement investing, open a Roth IRA first. For taxable investing, open a regular brokerage account. Fidelity, Vanguard, and Schwab are all excellent choices with no account fees.
2. Fund the account. Link your bank account and transfer money. Start with whatever you can, even $100.
3. Search for the fund. Type VTI, VOO, or SCHD in the search bar.
4. Place a buy order. Choose “market order” to buy at the current price. Enter the dollar amount (if fractional shares are available) or the number of shares.
5. Set up automatic contributions. Schedule a monthly automatic transfer and purchase. This is how dollar cost averaging works in practice.

For research and tracking your index fund investing portfolio, TradingView is the best tool available. You can chart performance, compare funds, and track your holdings in one place. Referred users get a $15 coupon on any paid plan.

Realistic Index Fund Investing Returns: What to Expect

The S&P 500 has averaged roughly 10% per year over the past century, about 7-8% after inflation. No individual year looks like 10%. Some years you’re up 25%. Some years you’re down 20%. But the long-term average has been remarkably consistent.

Here’s what index fund investing can realistically do with consistent monthly contributions:

$500 per month is $6,000 per year. That’s exactly the Roth IRA contribution limit for people under 50 right now. Max your Roth IRA with index fund ETFs starting at 25 and you could have $745,000 or more at 55, completely tax-free. That’s the power of index fund investing combined with tax advantaged accounts.

The Compounding Math Behind Index Fund Investing

$10,000 invested in the S&P 500 in 1990 would be worth roughly $240,000 by 2025 with dividends reinvested. No stock picking. No market timing. Just owning the index and waiting.

The compounding effect accelerates over time. In the first decade, growth feels slow. In the second decade, the gains start adding up noticeably. By the third decade, the account is generating more in investment returns each year than most people earn at their jobs.

At $500,000 invested and an 8% average annual return, your portfolio generates $40,000 per year in growth. You didn’t earn that through labor. You earned it because you started index fund investing early and stayed consistent.

How to Stay Consistent During Market Crashes

The biggest threat to index fund investing isn’t the market. It’s you. When markets drop 30% (and they will, periodically), every instinct tells you to sell. Don’t.

In 2020, the S&P 500 dropped 34% in five weeks. Six months later, it was at all-time highs. Investors who sold in March 2020 locked in those losses. Investors who kept buying got the full recovery. The most dangerous thing in index fund investing is trying to react to short-term events.

The best strategy: automate. Set up a monthly transfer and purchase. Remove the decision from your hands. When markets crash, your automatic buy buys more shares at lower prices. That’s dollar cost averaging working for you, which we cover in detail in the next piece of the wealth puzzle.

You can also read about how successful investors think about wealth in this post on why 95% of people never build real wealth. The mindset piece is just as important as the mechanics.

Start Index Fund Investing Today

Index fund investing doesn’t require timing, expertise, or large amounts of money to start. It requires consistency and patience. Open a Roth IRA. Buy VTI or VOO. Automate a monthly contribution. Reinvest dividends. Wait 20-30 years.

That’s the strategy. It’s boring. It works.

Disclosure: This post contains affiliate links. We may earn a commission at no extra cost to you.