You can buy index funds through a brokerage account in three steps: open an account with a broker, deposit money, and place an order for the index fund you want

The actual mechanics are straightforward. You pick a brokerage firm (Vanguard, Fidelity, Charles Schwab, and Robinhood are common ones), create an account online, link a bank account or transfer money in, then search for the index fund by its ticker symbol and buy shares. Most brokerages let you do this entirely on their website or app. The whole process usually takes less than an hour from start to finish.

The harder part is deciding which brokerage to use and which index fund to buy, because those choices affect how much you pay in fees and how your money grows over time. This guide walks through what to look for at each step.

Key Takeaways

  • You need a brokerage account to buy index funds; you cannot buy them directly from the fund company in most cases.
  • Different brokerages charge different fees, and some offer index funds with lower expense ratios than others.
  • You can start with as little as one share of an index fund, though many people invest a set amount monthly.
  • Index funds held in a regular taxable brokerage account are taxed on dividends and gains each year, but held in a retirement account (401k, IRA) they may grow tax-deferred.

Choosing a brokerage and opening an account

A brokerage is a company that lets you buy and sell investments. You open an account with them, deposit money, and use their platform to place trades. Most major brokerages now charge zero commission per trade, meaning you do not pay a fee just to buy or sell an index fund.

What differs between brokerages is the range of index funds they offer, the fees those funds charge, and the tools or research they provide. Vanguard, Fidelity, and Charles Schwab are large enough that they offer hundreds of index funds and have low fees across the board. Robinhood and some online-only brokers offer fewer funds but may appeal if you want a simpler interface.

To open an account, you will need your Social Security number, a valid ID, your address, and a bank account to link for deposits. The application takes about 10 minutes online. Most brokerages let you start trading within a day or two, though some require you to wait for a bank transfer to clear first.

Understanding index fund fees and expense ratios

Every index fund charges a yearly fee called an expense ratio, expressed as a percentage of the money you have invested. A fund with a 0.03% expense ratio costs you $3 per year for every $10,000 you have in it. A fund with a 0.50% expense ratio costs you $50 per year on the same $10,000.

This matters because over decades, a difference of 0.47% per year compounds into thousands of dollars in lost growth. Index funds from Vanguard, Fidelity, and Schwab typically have expense ratios between 0.03% and 0.20%. Some funds offered through other brokerages or older funds can charge 0.50% or higher. When you are comparing two index funds that track the same index, the one with the lower expense ratio is almost always the better choice.

You do not pay the expense ratio as a separate bill; it is deducted automatically from the fund's value each year. You will see it listed in the fund's prospectus or fact sheet, which the brokerage makes available before you buy.

Deciding how much to invest and how often

You can buy as little as one share of an index fund. If a share costs $400, you can invest $400. If it costs $50, you can invest $50. Some brokerages also offer fractional shares, meaning you can invest any dollar amount—$100, $250, $1,000—and own a proportional piece of the fund even if that amount does not equal a whole share.

Many people invest a fixed amount on a regular schedule—$200 per month, $500 per quarter, or a lump sum once a year. This approach, called dollar-cost averaging, means you buy more shares when prices are low and fewer when prices are high, which can reduce the impact of market swings over time. You can set up automatic monthly transfers from your bank account to your brokerage account, then buy the index fund on the same day each month.

There is no minimum amount you must invest at once, and no penalty for investing small amounts frequently. Start with whatever you can afford and increase it as your income grows.

Choosing which index fund to buy

An index fund tracks a specific market index—the S&P 500, the total U.S. stock market, international stocks, bonds, or some combination. Your choice depends on what you want your money to do and how much risk you are comfortable with.

A fund tracking the S&P 500 (ticker symbols like VOO, IVV, or SPY depending on the brokerage) gives you exposure to 500 large U.S. companies. A total U.S. stock market fund (VTI, ITOT, SWTSX) includes small and mid-sized companies too. An international stock fund (VXUS, IXUS, SWISX) adds exposure to companies outside the U.S. A bond fund (BND, AGG, SWAGX) is less volatile but typically grows more slowly.

Most people starting out choose either a single total U.S. stock market fund or a combination of a U.S. stock fund and an international stock fund. If you are young and can tolerate market swings, an all-stock approach is common. If you are closer to retirement or uncomfortable with volatility, adding bonds reduces the ups and downs.

Tax considerations for different account types

Where you hold an index fund matters for taxes. In a regular taxable brokerage account, you owe taxes each year on dividends the fund pays and on any gains when you sell shares for more than you paid. In a retirement account like a traditional IRA or Roth IRA, the money grows tax-deferred or tax-free, depending on the account type.

If your employer offers a 401(k) plan, you may be able to invest in index funds through that plan, and contributions reduce your taxable income for the year. If you do not have access to a 401(k) or want to invest beyond the annual limit, an IRA (traditional or Roth) lets you invest up to $7,000 per year (as of 2024, though this amount changes). A taxable brokerage account has no contribution limit but offers no tax advantage.

For most people, it makes sense to max out retirement accounts first because the tax benefits are substantial, then use a taxable account for additional investing. Index funds are tax-efficient compared to actively managed funds, so they are a good choice for taxable accounts too.

Placing your first trade and monitoring your investment

Once your account is funded, buying an index fund takes a few clicks. Search for the fund by its ticker symbol in your brokerage's search bar, select it, enter the dollar amount or number of shares you want to buy, and confirm the order. Most trades execute immediately during market hours (9:30 a.m. to 4 p.m. Eastern time on weekdays). You will see the purchase reflected in your account within minutes.

After you buy, you do not need to do much. Index funds are designed to be held long-term. Check your account balance occasionally if you want, but avoid the temptation to buy and sell based on short-term market movements. The longer you hold, the more time compound growth has to work in your favor. Most people who succeed with index funds invest regularly, ignore market noise, and leave their money alone for years or decades.

Frequently Asked Questions

Can I buy index funds without a brokerage account?

No. You must buy index funds through a brokerage, a bank, or an employer retirement plan. You cannot buy them directly from the fund company. Some employers offer index funds through their 401(k) plans, which is another route.

What is the minimum amount I need to start investing?

There is no universal minimum. Most brokerages let you open an account and buy a single share of any fund. If fractional shares are available, you can invest any dollar amount. Some brokerages have account minimums of $0 to $500, but many have none.

Do I have to reinvest dividends?

No, but most people do. When an index fund pays a dividend, you can choose to have the cash paid to you or automatically reinvested to buy more shares. Reinvestment accelerates growth over time and is usually the default option.

What happens if the market crashes after I invest?

Your account value will drop temporarily, but index funds recover over time because they own many companies across the economy. If you stop investing during a crash, you miss the opportunity to buy shares at lower prices. Continuing to invest through market downturns is one of the most powerful ways to build wealth with index funds.

Can I lose all my money in an index fund?

An index fund could theoretically fall to zero only if every company in that index went bankrupt simultaneously, which is extremely unlikely for broad indexes like the S&P 500 or total market funds. You can lose money in the short term if the market declines, but historically the market has recovered and grown over every 20-year period in U.S. history.