No — an index fund is a type of mutual fund, not the other way around

A mutual fund is a bucket of money from many investors that a fund manager uses to buy stocks, bonds, or other investments. An index fund is a specific kind of mutual fund that tracks a published list of investments — like the S&P 500 or the Nasdaq 100 — rather than having a manager pick individual holdings.

Think of it this way: all index funds are mutual funds, but not all mutual funds are index funds. A mutual fund could be actively managed (a person decides what to buy and sell), or it could be passively managed (it just copies an index). An index fund is always the passive kind.

Key Takeaways

  • A mutual fund pools money from many investors; an index fund is one category of mutual fund that tracks a specific published index instead of being actively managed.
  • Active mutual funds pay a manager to pick investments; index funds straightforward mirror an existing index like the S&P 500, which usually costs less in fees.
  • Index funds have lower turnover and lower expense ratios because no one is actively buying and selling holdings throughout the year.
  • Both mutual funds and index funds are held inside brokerage accounts, retirement accounts, or employer-sponsored plans like a 401(k).

How an active mutual fund works

In an active mutual fund, a fund manager and their team research companies, bonds, or other investments and decide what to buy and sell. They aim to beat the market — to earn returns higher than what a straightforward index would deliver. They might hold 50 stocks, or 200, depending on the fund's strategy.

Because someone is actively managing the fund, you pay for that work. The fund charges an expense ratio — a yearly fee taken from your account as a percentage of what you have invested. Active mutual funds typically charge between 0.5% and 2% per year, though some charge more.

The manager also buys and sells holdings throughout the year, which creates turnover. High turnover can trigger capital gains taxes inside the fund, which get passed to you as a shareholder.

How an index fund works

An index fund holds the same investments as a published index, in the same proportions. If you own a fund that tracks the S&P 500, you own a tiny piece of all 500 companies in that index, weighted by their market value. The fund does not try to beat the index — it tries to match it.

Because no manager is making individual stock picks, index funds have much lower expense ratios. Many charge 0.03% to 0.20% per year. That difference compounds over decades: on a $100,000 investment, paying 0.10% instead of 1.00% saves you roughly $900 per year.

Index funds also have low turnover. The holdings only change when the underlying index changes, which happens rarely. This means fewer capital gains taxes passed to shareholders.

Common index fund examples

An S&P 500 index fund holds all 500 companies in the Standard & Poor's 500 index. A total stock market index fund holds thousands of U.S. companies across all sizes. A bond index fund might track the Bloomberg Aggregate Bond Index. A total international index fund holds stocks from developed and emerging markets outside the United States.

Index funds exist for nearly every major market index. They are offered by major brokerages like Fidelity, Vanguard, and Charles Schwab, and they are common inside 401(k) plans and IRAs.

Why the distinction matters for your costs

The difference between active and index funds shows up most clearly in fees. Over 20 or 30 years, a 0.9% difference in annual fees can reduce your total return by tens of thousands of dollars, even if both funds earn the same market return before fees.

Research on active mutual fund performance shows that most active managers do not consistently beat their index over long periods, especially after fees are subtracted. This is why many investors choose index funds for the core of their portfolio — not because index funds are may provide to outperform, but because their lower costs make them a straightforward choice.

That said, some investors prefer active funds for specific reasons: a manager's track record in a particular sector, a fund's specific investment philosophy, or straightforward the belief that active management can add value in certain market conditions.

Where you hold mutual funds and index funds

Both types of funds live inside accounts. You might own them in a taxable brokerage account, where you pay taxes on gains and dividends each year. You might own them inside an IRA or Roth IRA, where growth is tax-deferred or tax-free. Many people own them through a 401(k) or similar employer plan, where the plan sponsor chooses which funds to offer.

The account type affects how taxes work, but it does not change how the fund itself operates. An index fund inside a 401(k) works the same way as an index fund in a brokerage account.

Frequently Asked Questions

Can an index fund outperform the index it tracks?

Slightly, yes — but usually only by a small amount. An index fund might earn a tiny bit more than its index because of cash held in the fund or reinvested dividends. It might also lag slightly due to fees. Over time, the fund's return should track very close to the index's return.

Are index funds safer than active mutual funds?

Not necessarily. Both hold the same types of investments — stocks, bonds, or a mix. An index fund that holds 500 large companies is not inherently safer than an active fund that holds 50 large companies; it is just more diversified. The safety depends on what the fund holds, not whether it is actively or passively managed.

Can I switch from an active mutual fund to an index fund?

Yes. If you own an active fund in a taxable account, selling it may trigger capital gains taxes, so check with a tax professional first. Inside a 401(k) or IRA, you can usually switch between funds without tax consequences. Contact your fund provider or plan administrator to make the change.

Do index funds ever change what they hold?

Yes, but rarely. When a company is added to or removed from the underlying index, the index fund adjusts its holdings to match. For example, when a company joins the S&P 500, an S&P 500 index fund buys shares of that company. These changes happen a few times per year at most.

What is the cheapest type of mutual fund?

Index funds are typically the cheapest because they require no active management. Within index funds, larger funds and those offered by major brokerages often have the lowest expense ratios. Some index funds charge less than 0.05% per year.