Index funds are the simplest way to invest in the stock market. Instead of picking individual stocks, you buy a small piece of hundreds or thousands of companies at once. This guide explains how index funds work, why most experts recommend them, and how to buy your first one today.
What Is an Index Fund?
An index fund is an investment that tracks a market index. An index is just a list of companies. The S&P 500, for example, is a list of 500 large U.S. companies. An S&P 500 index fund owns shares of all 500 companies in proportion to their size.
When the S&P 500 goes up, your fund goes up. When it goes down, your fund goes down. You are not trying to beat the market — you are trying to match it.
Why Index Funds Beat Most Investors
Over any 20-year period, roughly 90% of actively managed funds underperform their benchmark index. Fund managers who try to pick winning stocks, on average, do worse than just owning the whole market.
The reason is simple: costs. An actively managed fund might charge 1.00% per year in fees. An index fund charges 0.03% to 0.10%. That difference compounds over decades and takes a serious bite out of your returns.
Types of Index Funds
Total Market Index Funds
These funds own every publicly traded U.S. company. They give you maximum diversification in one fund. Examples: Vanguard Total Stock Market Index Fund (VTSAX), Fidelity ZERO Total Market Index Fund (FZROX).
S&P 500 Index Funds
These funds own the 500 largest U.S. companies. They cover about 80% of the total U.S. stock market value. Examples: Vanguard 500 Index Fund (VFIAX), Fidelity 500 Index Fund (FXAIX), iShares Core S&P 500 ETF (IVV).
International Index Funds
These funds own companies outside the U.S. Adding international exposure diversifies your portfolio beyond one country’s economy. Example: Vanguard Total International Stock Index Fund (VTIAX).
Bond Index Funds
Bond funds own government or corporate bonds. They are less volatile than stock funds and help balance your portfolio as you get closer to retirement. Example: Vanguard Total Bond Market Index Fund (VBTLX).
How to Buy an Index Fund: Step by Step
Step 1: Open a Brokerage Account
You need an account to buy funds. Good options for beginners:
- Fidelity — no minimums, strong customer service, ZERO expense ratio funds
- Vanguard — the original index fund company, owned by its investors
- Charles Schwab — no minimums, good mobile app
Step 2: Choose the Right Account Type
If you are investing for retirement, open an IRA. A Roth IRA lets your money grow tax-free. A traditional IRA gives you a tax deduction today. If you might need the money before retirement, open a regular taxable brokerage account.
Step 3: Fund Your Account
Link your bank account and transfer money. Most brokerages process transfers in one to three business days.
Step 4: Search for Your Fund
Use the fund’s ticker symbol to find it. FXAIX, VFIAX, and VOO are all S&P 500 index funds. Each has slightly different minimums and expense ratios.
Step 5: Buy Shares
Enter the dollar amount you want to invest and place the order. Many brokerages let you buy fractional shares, so you can invest any amount even if one share costs $400+.
How Much Should You Invest?
There is no minimum. Start with whatever you can. Investing $50 per month beats investing $0 per month. The key is consistency. Set up automatic contributions so you invest the same amount every month without thinking about it.
Over 30 years, $200 per month invested in an S&P 500 index fund earning 10% annually grows to about $452,000. That is the power of compound interest working over time.
Common Mistakes to Avoid
- Waiting for the “right time.” Time in the market beats timing the market. Start now.
- Selling during downturns. Market drops are normal. Selling locks in your losses.
- Paying too much in fees. Every dollar in fees is a dollar that does not compound for you.
- Buying too many funds. Three to four index funds can cover the entire global market. You do not need 20 funds.
Bottom Line
Index funds are the simplest, lowest-cost way for most people to build wealth through investing. You do not need to be an expert. You do not need a financial advisor. You need a brokerage account, a paycheck, and the discipline to invest consistently and leave it alone.