Index funds are bought through a brokerage account, not directly from the fund company

You cannot buy an index fund the way you buy a stock. Instead, you open an account with a brokerage — a company that holds your money and executes trades on your behalf. The brokerage is the intermediary between you and the fund. Popular brokerages include Fidelity, Vanguard, Charles Schwab, and E-Trade, though many others exist. Once your account is open and funded, you search for the index fund you want by its ticker symbol (a short code like SPY or VOO), and place an order to buy shares.

The brokerage charges you a fee for holding your account, though many now offer commission-free trading on index funds. Some brokerages charge an annual account fee if your balance falls below a minimum; others charge nothing at all. Read the fee schedule before you open an account, because fees compound over decades and eat into your returns.

You will need to provide your Social Security number, proof of address, and banking information so the brokerage can transfer money in and out. The whole process usually takes 10 to 15 minutes online.

Key Takeaways

  • You buy index funds through a brokerage account, not from the fund company directly, and most brokerages now charge no commission per trade.
  • Opening an account requires your Social Security number, proof of address, and a bank account to link for deposits and withdrawals.
  • Different brokerages charge different annual fees and have different minimum balances, so comparing them before you open saves money over time.
  • You can buy index funds inside a regular taxable account or inside a tax-advantaged account like a 401(k) or IRA, and the tax treatment differs significantly.
  • Index funds are bought and sold during market hours at the closing price of the day you place your order, not at the price you see on your screen.

Choosing between a taxable account and a tax-advantaged account

A taxable brokerage account is the simplest route: you deposit money, buy index funds, and pay taxes on any gains when you sell or receive dividends. You can withdraw money anytime without penalty. There is no annual contribution limit. This account makes sense if you are saving for something within the next five years, or if you have already maxed out tax-advantaged accounts.

A 401(k) is an employer-sponsored retirement account. Your employer may match a portion of what you contribute (usually 3 to 6 percent of your salary), which is assistance programs. Contributions come out of your paycheck before taxes, lowering your taxable income that year. You cannot withdraw the money before age 59½ without paying a 10 percent penalty plus income tax, with narrow exceptions. If your employer offers a 401(k), this is usually the best place to start because of the employer match.

An IRA (Individual Retirement Account) is a retirement account you open yourself, not through an employer. A Traditional IRA works like a 401(k): contributions may be tax-deductible, and you pay taxes when you withdraw in retirement. A Roth IRA works differently: contributions are made with after-tax money, but withdrawals in retirement are tax-free. For 2024, you can contribute up to $7,000 per year to an IRA (or $8,000 if you are 50 or older). An IRA makes sense if your employer does not offer a 401(k), or if you have already contributed the maximum to your 401(k).

The tax advantages of retirement accounts mean your money grows without being taxed each year, which compounds significantly over decades. The tradeoff is that you cannot access the money without penalty until retirement age.

How to fund your account and place your first order

After you open your brokerage account, you link a bank account and transfer money in. This transfer usually takes one to three business days. Some brokerages let you start trading immediately with a "margin" feature, but as a new investor you should wait for the money to settle.

Once the money is in your account, search for the index fund you want by its ticker symbol. The brokerage will show you the fund's current price, expense ratio (the annual fee charged by the fund company), and performance history. Read the fund's prospectus — a legal document that explains what the fund holds and how it works — before you buy. Most brokerages have a link to the prospectus on the fund's page.

When you place an order, you specify how many shares you want to buy. The order executes at the market close that day (usually 4 p.m. Eastern time). You will see the exact price you paid only after the order settles, which is typically the next business day. Do not panic if the price has moved slightly between when you placed the order and when it settled; this is normal.

You can set up automatic monthly or weekly transfers from your bank account to your brokerage, and then set up automatic purchases of the same index fund on the same schedule. This removes the temptation to time the market and keeps you investing consistently.

Understanding expense ratios and why they matter

Every index fund charges an annual fee called the expense ratio, expressed as a percentage of your balance. A fund with a 0.03 percent expense ratio charges $3 per year on every $10,000 you have invested. A fund with a 1 percent expense ratio charges $100 per year on the same $10,000.

This difference seems small, but it compounds. Over 30 years, a 0.03 percent expense ratio versus a 1 percent expense ratio can mean tens of thousands of dollars in lost returns on a six-figure portfolio. Always choose the lowest-cost version of the index you want to track. Vanguard, Fidelity, and Schwab all offer index funds with expense ratios below 0.10 percent.

Some brokerages offer their own index funds with lower fees than competitors' versions of the same index. For example, Vanguard's S&P 500 index fund (ticker VOO) has a lower expense ratio than Fidelity's version (ticker FXAIX), though both track the same index. Compare the expense ratios of the funds available at your chosen brokerage before you buy.

What happens after you buy: monitoring and rebalancing

After you buy an index fund, you do not need to do anything. The fund automatically rebalances itself to stay true to its index. You will receive dividends (usually quarterly), which the brokerage can reinvest automatically into more shares of the same fund, or you can take as cash.

Check your account balance quarterly or annually, but do not check it daily. Daily price swings are noise and will tempt you to sell at the wrong time. Index funds are designed to be held for years or decades, not traded frequently.

If you are contributing to multiple accounts (a 401(k) and an IRA, for example), you may end up holding the same index fund in both places. This is fine and actually simplifies your portfolio. If you are holding different index funds across accounts, review them once a year to make sure they still match your overall strategy.

Common mistakes new index fund investors make

The most common mistake is buying too many different index funds. A new investor might buy a U.S. stock index fund, an international stock index fund, a bond index fund, and a real estate index fund all at once, then panic-sell when one of them drops 10 percent. Start with one or two broad index funds and add complexity only after you understand how they behave.

The second mistake is trying to time the market. New investors often wait for a price drop before buying, or sell when prices rise. Research shows that staying invested through market cycles beats trying to predict them. If you have money to invest, invest it now rather than waiting for a "better" price.

The third mistake is paying too much in fees. Some brokerages charge $5 to $10 per trade, or annual account fees of $50 or more. Others charge nothing. There is no reason to pay these fees when commission-free brokerages exist. Similarly, some index funds have expense ratios above 0.50 percent when identical funds cost 0.03 percent. Over 30 years, this difference is enormous.

The fourth mistake is not taking advantage of tax-advantaged accounts. If your employer offers a 401(k) match, not contributing enough to get the full match is leaving assistance programs on the table. Prioritize getting the full match before investing in a taxable account.

Frequently Asked Questions

Do I need a lot of money to start investing in index funds?

No. Most brokerages have no minimum deposit, and you can buy fractional shares of index funds, meaning you can invest $50 or $100 and own a piece of a fund that costs more per share. Start with whatever amount you can afford and increase it over time.

Should I buy index funds in a 401(k) or a regular brokerage account?

Prioritize your 401(k) first, especially if your employer matches contributions — that match is immediate assistance programs. Once you have contributed enough to get the full match, you can open an IRA or taxable brokerage account. If you do not have an employer 401(k), open an IRA before a taxable account.

What if the market crashes right after I buy index funds?

Market crashes are normal and happen roughly every 10 years. If you are investing for retirement (10+ years away), a crash is actually good news because you can buy more shares at lower prices. If you need the money within five years, index funds are not the right investment for you.

Can I lose all my money investing in index funds?

An index fund can drop significantly in value, but it cannot go to zero unless every company in the index fails simultaneously, which has never happened. Broad index funds like the S&P 500 are diversified across hundreds of companies, so individual company failures do not wipe out your investment.

How often should I buy more index fund shares?

Consistency matters more than timing. Monthly or quarterly automatic purchases work well for most people because they remove emotion from the decision and spread your purchases across different market prices. You can also make larger purchases when you receive bonuses or tax refunds.