Mutual funds

A mutual fund is a pool of money from many investors, used to buy a big basket of investments that everyone in the pool owns together. Buy in and you own a small slice of everything the fund holds. It's one of the most common investments in the world, and if you ever save for retirement through a job, it's probably the first one you'll meet.

One pool, hundreds of holdings

Imagine 1,000 people each put $100 into a shared pot. The pot now holds $100,000 — enough to buy shares in hundreds of different companies, far more than any single $100 could. Each person owns their fraction of the whole basket: put in $100 and you own a tiny piece of every holding.

That spreading-out is diversification — money across many investments, so no single one can sink you. If one company in the basket fails, your loss is limited to your small slice of it. It doesn't make losses impossible, though. If the whole basket drops 10% in a rough market, your $100 becomes $90 — every slice fell together.

Priced once a day, after the close

A share of a company changes price all day long. A mutual fund doesn't. Once a day, after the market closes, the fund adds up the value of everything it owns, divides by the number of fund shares, and that's the day's price. Everyone who put money in that day gets the same price.

That changes how you buy. You don't order a number of shares at a moment's price — you send in a dollar amount, like $50, and after the close the fund credits you the matching number of shares, fractions included. There's no moment to pick, so there's nothing to time.

Who decides what goes in the basket

There are two basic approaches. In an actively managed fund, a professional manager picks investments they believe will beat the market. In a passively managed fund, nobody picks — the fund follows a fixed list or formula. The most common version is an index fund, which holds everything in an index: a defined list of investments used to measure a market, like the 500 large U.S. companies in the S&P 500.

Here's the part that trips people up: "mutual fund" describes the package, not the strategy. A mutual fund can be actively managed, and a mutual fund can be an index fund. The two labels answer different questions — how you buy it, and what's inside.

Management isn't free either way. A fund's expense ratio is its annual fee, charged as a percent of your money whether the fund gains or loses. Active management costs more, because you're paying for the manager's work — and whether that extra cost earns itself back is something people who study funds genuinely disagree about.

Where you'll actually meet one

The most common place is a retirement plan at work. A 401(k) is a retirement account through an employer, funded straight from your paycheck — and its menu of investment choices is usually a list of mutual funds. Your employer picks the menu; you pick from it. Once-a-day pricing fits that job: retirement money goes in a little each payday, on a schedule, and nobody needs to pick a moment.

Mutual funds and ETFs

You'll often see mutual funds mentioned next to an exchange-traded fund (ETF) — a pooled fund that trades all day like a stock. The two can hold the exact same investments. The difference is mechanical. An ETF's price moves while the market is open, and you buy shares at whatever the price is when your order goes through. A mutual fund prices once, after the close, and you buy with a dollar amount.

Neither package is better. They're two doors into the same room, and which door you use usually comes down to what your account offers.