Index funds

In short

A friend of mine once told me he felt left out because he could not name a single stock to buy. If you have ever felt the same way, you are in good company, and you may like what an index fund does. It holds a small slice of every company on a list, so no one has to pick winners. The fee is the main thing you control, so look for it first, and then read the fund's prospectus, the plain document that lists its costs and rules. Start with a small sum you can leave alone for many years. No cleverness required.

The whole of it

What it is

I once watched my neighbor try to pick the best peach from a crate of two hundred. He squeezed, he sniffed, he turned each one over like a man appraising a horse, and he walked away with one that was mealy inside. An index fund takes a different road. It buys a little of every peach in the crate and takes the average.

An index is a list of companies, kept by a firm that sets the rules for who gets on it. The S&P 500, for example, is a list of large American companies. An index fund is built to copy such a list. If the list holds five hundred companies, the fund holds pieces of those five hundred, and when the list changes, the fund changes with it. Simple enough.

You will find index funds in two common shapes. A mutual fund is bought straight from the fund company, and it trades once a day after the market closes. An exchange traded fund, called an ETF, trades all day on the stock market like a single share. Both can follow the same index. The difference is mostly in how a person buys and sells.

How it works

If you are holding a retirement account, you may already own an index fund without knowing it. Many plans offer one, and many target date funds are built from them, so it is worth a quick look at your own statement. Here is how the machinery turns.

The fund company gathers money from many investors. It uses that money to buy the companies on the list, in the same proportions the list uses. A bigger company gets a bigger share, because the list is usually weighted by size. Nobody at the fund is hunting for bargains. The job is to match the list, which takes less work than guessing.

Less work means a smaller charge. The fee is called the expense ratio, and it is a yearly percent of what you hold. The fund takes it out of the fund's assets, so no bill ever shows up in your mailbox. A fee of 0.1 percent means $1 a year for every $1,000 you hold. Small. But it comes around every single year, and a small thing repeated for decades can grow into something a person would be sorry to have ignored.

The fund also passes along money the companies pay out. Companies send some of their profit to shareholders as dividends, and the fund hands these on to you or reinvests them, as you choose. A fund that trades very little also tends to create fewer taxable events, which is one reason many people hold these funds in a regular account.

The numbers, and where to find yours

You have probably wondered where to look for the facts. Good news, because every fund has to publish them. The place to start is the fund's prospectus, a document filed with the Securities and Exchange Commission, the federal agency that oversees funds. Any fund can be searched on the SEC's EDGAR database. The fund company's own website shows the same figures near the top of the fund page.

The first number to find is the expense ratio. Find the second as well, which is the minimum to open the fund. Some funds ask for $3,000 to start, and some ask for nothing at all. If you are saving inside a retirement account, the yearly contribution limit is $7,500 for 2026 (source, checked 10/4/2026), and the plan's own rules decide which funds a saver may pick. The same fund page lists the index it follows, along with a few holdings at the top.

One more figure is worth your time. Funds report how closely they tracked their index, sometimes called tracking difference. A fund that charges more will usually trail its index by about that much. Put two funds side by side that follow the same list, and the cheaper one keeps more for the saver.

A worked example

Let me tell you about a woman I will call Maria, who is thirty five and has $20,000 to invest. She sees two funds that follow the same index. Fund A charges 0.05 percent a year, and Fund B charges 1.00 percent a year. To keep the arithmetic plain, say both earn 7 percent a year before fees, and Maria adds nothing more.

Fund A takes 0.05 percent, so Maria keeps 6.95 percent a year. Fund B takes 1.00 percent, so she keeps 6.00 percent a year.

After thirty years in Fund A, the math is $20,000 times 1.0695 raised to the thirtieth power. That power is about 7.63, so the total is $20,000 times 7.63, which is about $152,600.

After thirty years in Fund B, the math is $20,000 times 1.06 raised to the thirtieth power. That power is about 5.74, so the total is $20,000 times 5.74, which is about $114,800.

The gap is $152,600 minus $114,800, or about $37,800. Maria put in the same $20,000 both times, and the only change was the fee. That is a great deal to hand over for no reason at all.

The yearly fee looks tiny when it is first charged. On $20,000, Fund A takes 0.05 percent, which is $10 a year at the start. Fund B takes 1.00 percent, which is $200 a year at the start. Small bites, repeated for thirty years. These figures are made up to show the method, and real returns will differ every year.

Where it goes wrong

I have made a few mistakes in my own life, and the quiet ones cost the most. The first trap is thinking all index funds are alike. Two funds can follow different lists. One may hold only large companies, and another may hold only a narrow slice, like a single industry. The name on the fund can hide this, so the list itself is worth reading.

The second trap is the fee. Two funds on the same list can charge very different amounts, as Maria saw. Check the expense ratio, and check for any sales charge, which some funds call a load. Index funds do not need one.

A third trap is the trading itself. An ETF trades like a share, and a person who trades often can pay spreads, which is the small gap between the buying price and the selling price. Some brokers charge fees too. Buying and selling in a panic is where many people get hurt. Slow down.

Fourth, an index fund does not shield anyone from a falling market. If the whole list drops, the fund drops with it. That is no flaw in the fund. Copying a list means copying its bad days along with its good ones, and I would be doing you no kindness if I pretended otherwise.

Last, taxes. In a regular account, dividends and gains can be taxed in the year they happen. A retirement account follows its own tax rules. Read the rules for the account in question, and ask a tax professional if the answer is unclear.

Questions to answer before you leave this page

What is the money for, and when will you need it? Which index does the fund follow, and do you know what is on that list? What is the expense ratio, and what would it cost you in dollars each year on the amount you plan to put in? Is the fund a mutual fund or an ETF, and do you understand how each one is bought and sold? Does the fund have a minimum, a load, or any other charge that you missed in the prospectus? Will this sit in a retirement account or a regular account, and what are the tax rules for that choice? Can you leave the money alone through a bad year without selling in a hurry?