Index Funds Explained

What Is an Index?

A stock market index is just a list. The S&P 500 is a list of 500 large U.S. companies. The total market index is a list of roughly 3,500–4,000 U.S. companies. These lists are maintained by financial companies and updated periodically as companies grow, shrink, or go out of business.

An index fund is an investment that tracks one of these lists. It buys all (or nearly all) the stocks in the index in proportion to their size. When you invest in an S&P 500 index fund, you automatically own a tiny piece of Apple, Microsoft, Amazon, Google, and 496 other companies — all at once.

Why Not Just Pick Good Stocks?

The intuitive approach is to pick the companies you think will do well. The problem is that professional fund managers — people who do this full time with research teams and decades of experience — fail to consistently beat a simple index fund.

Studies show that over 10–15 year periods, more than 85–90% of actively managed funds underperform their benchmark index. The ones that do beat it in one period rarely repeat it in the next.

Why? Markets are competitive. By the time information is public, it's already priced in. The fund managers who beat the market one year are largely doing so due to luck, not skill — and they charge you 0.5–1.5% per year for the privilege of underperforming.

The Cost Advantage

Index funds are cheap to run because no one is making active decisions — the fund just holds whatever the index holds. That means extremely low fees.

That difference compounds dramatically over decades. On a $100,000 portfolio over 30 years at 7% return:

• At 1.0% annual fee: final value ≈ $574,000
• At 0.04% annual fee: final value ≈ $747,000

The fee difference alone costs you over $170,000.

Types of Index Funds

By what they track

Mutual funds vs. ETFs

Index funds come in two flavors:

Mutual funds (e.g., VTSAX, FSKAX) — bought directly from the fund company at end-of-day price, often have a minimum investment ($3,000 for Vanguard's VTSAX).

ETFs (e.g., VTI, SCHB) — trade like stocks on an exchange throughout the day, usually no minimum investment beyond one share price. Functionally identical to the mutual fund versions for long-term investors.

For most beginners, the choice between them doesn't matter. Just pick whichever has no minimum requirement at the broker you use.

What to Buy

For most people starting out, one of these covers everything you need:

If you want international exposure (generally a good idea for diversification), add:

• Fidelity: FZILX or FTIHX
• Vanguard: VXUS
• Schwab: SCHF

A simple two-fund portfolio — total U.S. market + total international — is genuinely all most people need for decades.

How to Actually Buy One

1. Open an account — Roth IRA, 401(k), or taxable brokerage at Fidelity, Vanguard, or Schwab
2. Transfer money into the account
3. Search for the fund ticker (e.g., FZROX)
4. Enter the dollar amount you want to invest
5. Confirm the purchase

That's it. Set up automatic recurring investments if you can. Then leave it alone.

The Most Important Thing

Index funds work best when you don't touch them. The temptation during a market drop is to sell. The investors who keep buying consistently through downturns — and never sell in a panic — are the ones who capture the full long-term return. The fund's strategy is simple; the hard part is sticking to it.

FAQ

Are index funds safe?

They're not risk-free — they fall when the market falls. In 2008–2009, the S&P 500 dropped about 50%. But over every 15–20 year period in history, U.S. stock market index funds have recovered and reached new highs. The risk is short-term volatility, not permanent loss (for diversified, broad-market funds).

Is one index fund enough?

A total market index fund is broadly diversified by itself. Many people hold just one fund (like VTI) for their entire investing life and do extremely well. Adding international exposure (VXUS) reduces concentration in U.S. markets, which is generally worth doing.

What's the difference between an index fund and a target date fund?

A target date fund (e.g., Vanguard Target Retirement 2055) holds index funds inside it and automatically shifts from stocks to bonds as you approach retirement. It's a complete, self-managing portfolio in a single fund. Great for people who want zero maintenance — slightly higher fee than buying the underlying index funds separately.