What is an index fund?

An index fund is a type of investment that tracks a specific market index — the most commonly cited example is the S&P 500, which represents 500 of the largest publicly traded companies in the United States.

Instead of a fund manager picking stocks based on research or predictions, an index fund simply holds every stock in the index in proportion to its size. It does not try to beat the market. It tries to be the market.

This sounds boring. It has made a lot of ordinary people wealthy over time.

Why index funds outperform most active investing

Decades of data have established something counterintuitive: the majority of professional fund managers fail to beat simple index funds over long time horizons.

The S&P 500 Indices Versus Active (SPIVA) scorecard, published annually, consistently shows that over 10–15 year periods, more than 80–90% of actively managed US equity funds underperform their benchmark index.

The reasons are structural: 1. Costs compound against you. Active funds charge 0.5–1.5% per year in fees. Index funds charge 0.03–0.20%. That gap compounds over decades. 2. Taxes. Active funds trade more frequently, generating taxable events. Index funds rarely sell. 3. Survivorship bias. When studies compare "active funds" over 20 years, they forget to include the funds that closed due to poor performance.

How to buy your first index fund

Step 1: Open a brokerage account

You need a brokerage account to buy index funds. In the US, the major low-cost options are:

  • Fidelity — No minimum, excellent index fund selection, good app
  • Vanguard — Invented the index fund concept, competitive fees
  • Charles Schwab — Good selection, no minimums, strong customer service
For retirement accounts specifically, open a Roth IRA (if you are under the income limit) or a traditional IRA.

Step 2: Pick a fund

For US market exposure:

  • Fidelity ZERO Total Market Index Fund (FZROX) — 0.00% expense ratio
  • Vanguard Total Stock Market ETF (VTI) — 0.03% expense ratio
  • iShares Core S&P 500 ETF (IVV) — 0.03% expense ratio
For global diversification:
  • Vanguard Total World Stock ETF (VT) — 0.07% expense ratio

Step 3: Set up automatic contributions

The single most powerful action you can take is automating a fixed dollar amount into your index funds every payday. This is called dollar-cost averaging. You buy more shares when prices are low, fewer when prices are high.

Common mistakes to avoid

Checking your balance during market downturns. The instinct to sell when markets drop 20–30% is hardwired. It is also the most expensive mistake individual investors make.

Waiting for the "right time to invest." The data consistently shows that investing regularly (not timing the market) is the better approach.

Paying unnecessary fees. Expense ratios above 0.50% are hard to justify for index funds.

The bottom line

Index funds are not exciting. What they have is a long track record of outperforming the vast majority of active strategies, at a fraction of the cost, requiring minimal time or expertise.