ETFs vs Index Funds vs Mutual Funds: What's the Difference?

The words get used as if they mean the same thing, and they overlap, which is why this is confusing. The trick is to see that they answer two different questions:

1. What does the fund try to do? (Pick investments, or copy an index?)
2. How do you buy and sell it? (On an exchange all day, or once a day from the fund company?)

First: what is a fund?

A fund pools money from thousands of people and uses it to buy a collection of investments, like stocks or bonds. Each person owns a slice of the whole collection.

The big advantage is diversification: with one purchase you can own hundreds or thousands of companies, so one company’s bad news has a much smaller effect on you. It’s the investing version of not putting all your eggs in one basket.

Index funds: a strategy

An index is a list of companies chosen by a rule. The S&P 500, for example, tracks around 500 large U.S. companies. An index is just a measurement; you can’t invest in it directly.

An index fund simply tries to copy an index: it holds the same companies in roughly the same proportions. No one is trying to pick winners. Because there’s little research or trading involved, index funds tend to have low fees.

The opposite approach is an actively managed fund, where a manager picks investments hoping to beat the market. That costs more, and many active funds don’t beat their index after fees over long periods.

ETFs and mutual funds: two ways to package a fund

Mutual funds are bought and sold directly through the fund company (or a broker) once a day. Every order placed during the day gets the same price, calculated after the market closes.

ETFs (exchange-traded funds) trade on a stock exchange throughout the day, just like individual stocks. The price can change minute by minute, and you buy from and sell to other investors.

So an index fund can come as either a mutual fund or an ETF. Many of the most popular ETFs are index funds.

	Mutual fund	ETF
How you trade it	Through the fund company or a broker	On a stock exchange, like a stock
When you trade	Once a day, at the closing price	Any time the market is open
Can it be an index fund?	Yes	Yes
Minimum investment	Sometimes a set minimum	Usually the price of one share, or less with fractional shares

Why fees matter more than they look

Every fund charges an annual fee called the expense ratio, taken as a percentage of what you have invested. It looks tiny, but it’s charged every year on your whole balance.

A simple illustration: imagine $10,000 growing at 6% a year before fees for 30 years.

• With a 0.1% annual fee, it grows to roughly $55,800.
• With a 1.0% annual fee, it grows to roughly $43,200.

Same starting amount, same market. The difference of about $12,600 is the cost of the higher fee compounding over three decades. (These numbers are an example, not a prediction of any real return.)

Common questions

Is an ETF safer than a stock? An ETF that holds many companies is more diversified than a single stock, so one company failing hurts less. But a fund still rises and falls with the market it holds, and it can lose value.

Are all ETFs index funds? No. Many are, but some ETFs are actively managed or focus on narrow themes, which can be riskier and more expensive.

What should I look at on a fund’s page? What it holds, the index it tracks (if any), and its expense ratio are good places to start.

The one thing to remember

“Index fund” is what a fund does; “ETF” or “mutual fund” is how it’s packaged. And whatever the package, the annual fee quietly compounds against you.