How to buy index funds through a brokerage account

To invest in index funds, you open an account with a brokerage firm, deposit money, and place an order to buy shares of a specific index fund. The brokerage holds your account and executes the trades. You can open an account online in under an hour with most brokerages — you'll need your Social Security number, proof of address, and a bank account to link for deposits.

The actual purchase works like buying a stock: you log into your account, search for the index fund by its ticker symbol (a short code like SPY or VTI), decide how many shares you want, and submit the order. The order executes during market hours, usually within seconds. Your account then shows you as the owner of those shares, and you can hold them as long as you want or sell them whenever you choose.

Different brokerages charge different fees. Some charge a flat commission per trade (often $5 to $10), while others offer commission-free trading on index funds. Some also charge an account maintenance fee if your balance falls below a minimum, typically $500 to $2,500. Before opening an account, check the fee structure on the brokerage's website — it's usually listed under "Pricing" or "Fees."

Key Takeaways

  • You need a brokerage account to buy index funds; common brokerages include Fidelity, Vanguard, Charles Schwab, and E-Trade, and many now offer commission-free trades.
  • Opening an account requires your Social Security number, proof of address, and a linked bank account, and takes about an hour online.
  • You buy index funds by searching for the fund's ticker symbol in your account, entering the number of shares you want, and submitting the order during market hours.
  • Fees vary by brokerage and fund type; compare commission costs and account minimums before choosing where to open your account.
  • Index funds are meant to be held for years, not traded frequently, so focus on finding a low-cost fund that matches your time horizon rather than timing the market.

Choosing between a regular brokerage account and a retirement account

A regular brokerage account (also called a taxable account) has no contribution limits and no restrictions on when you can withdraw money. You pay taxes on any gains when you sell the fund, and you pay taxes on dividends the fund distributes each year. This account makes sense if you're investing money you may need before retirement or if you've already maxed out retirement account contributions.

A retirement account — such as a Traditional IRA, Roth IRA, or 401(k) — offers tax advantages. With a Traditional IRA or 401(k), you may deduct contributions from your taxes in the year you make them, and you don't pay taxes on gains until you withdraw money in retirement. With a Roth IRA, you pay taxes on contributions now, but withdrawals in retirement are tax-free. Retirement accounts have annual contribution limits (for 2024, IRAs allow $7,000 per year for most people under 50, and 401(k)s allow $23,500), and you generally cannot withdraw money before age 59½ without a penalty.

Most people should prioritize retirement accounts first — especially if an employer offers a 401(k) match, which is assistance programs. Once you've contributed enough to capture any match and maxed out an IRA if you want to, a regular brokerage account is the next place to invest. You can hold index funds in either type of account; the difference is the tax treatment, not the investments themselves.

Setting up automatic monthly investments

Most brokerages allow you to set up automatic transfers from your bank account to your investment account on a schedule you choose — weekly, monthly, or quarterly. This is called dollar-cost averaging, and it removes the need to decide when to invest. Instead of trying to time the market, you invest the same amount on the same day each month, which smooths out the effect of price changes over time.

To set up automatic investing, log into your brokerage account, find the "Transfers" or "Automatic Investments" section, and link your bank account if you haven't already. Then choose the amount, frequency, and the index fund you want to buy. Some brokerages let you set this up in minutes; others require you to call. Once it's running, the money moves automatically and buys shares at whatever price the fund is trading at that day.

Automatic investing is especially useful if you're investing for retirement and plan to hold for decades. It removes emotion from the process and ensures you keep investing even when markets are down — which is when prices are lowest and your money buys more shares.

Understanding fund expense ratios and total costs

Every index fund charges an expense ratio, which is an annual fee expressed as a percentage of your investment. For example, a fund with a 0.03% expense ratio costs $3 per year for every $10,000 you have invested. This fee is deducted automatically from the fund's value; you don't write a check for it.

Expense ratios vary widely. Passive index funds typically charge 0.03% to 0.20% per year, while actively managed funds often charge 0.50% to 1.50% or more. Over decades, even small differences add up. A $10,000 investment growing at 7% annually costs you about $3,000 more over 30 years if the expense ratio is 1% instead of 0.03%.

When comparing index funds, look at the expense ratio first. Vanguard, Fidelity, and Schwab all offer low-cost index funds with expense ratios under 0.10%. You can find the expense ratio on the fund's fact sheet, which every brokerage displays when you search for the fund. Some brokerages also charge trading commissions on top of the expense ratio, though most major brokerages now offer commission-free index fund trades.

What happens after you buy: monitoring and rebalancing

After you buy index funds, you don't need to do much. Index funds are designed to track a market index passively, so they don't require active management. You can check your account balance whenever you want, but daily price changes are normal and don't require action. Most investors check their accounts quarterly or annually.

Over time, if you own multiple index funds, their values may grow at different rates, and your portfolio may drift away from your original target allocation. For example, if you wanted 60% stocks and 40% bonds, but stocks grew faster, you might end up with 65% stocks and 35% bonds. Rebalancing means selling some of the funds that have grown too large and buying more of the ones that have shrunk, to return to your target mix. You can rebalance once a year or every few years; there's no single right answer.

If you're making regular monthly investments, you can rebalance by directing new contributions toward whichever fund is underweight. This avoids selling and triggering taxes in a taxable account. If you're in a retirement account, you can rebalance without tax consequences, so the method doesn't matter as much.

Common mistakes to avoid when starting out

The biggest mistake is trying to time the market — waiting for prices to drop before investing, or pulling money out when markets fall. Markets are unpredictable, and missing even a few of the best days can cut your long-term returns significantly. If you're investing for retirement, ignore short-term price swings and stick to your plan.

A second mistake is chasing performance. You might see that one index fund returned 15% last year while another returned 8%, and want to switch to the winner. But past performance doesn't predict future results, and switching often means selling low and buying high. Pick a low-cost index fund that matches your goals and time horizon, then leave it alone.

A third mistake is holding too much cash while waiting for the "right time" to invest. Time in the market beats timing the market. If you have money to invest and a long time horizon, start now. If you're nervous about a lump sum, automatic monthly investing lets you ease in gradually.

Finally, don't neglect fees. A fund charging 1% instead of 0.10% costs you tens of thousands over decades. Always check the expense ratio and trading commissions before opening an account or buying a fund.

Frequently Asked Questions

How much money do I need to start investing in index funds?

Most brokerages have no minimum to open an account, though some require $500 to $2,500 to avoid a maintenance fee. You can start with as little as $1 if you're willing to pay the fee, or wait until you have enough to avoid it. Many brokerages waive minimums if you set up automatic monthly deposits, so check the specific brokerage's rules.

Can I lose all my money investing in index funds?

Index funds can decline in value — sometimes sharply — but they're unlikely to go to zero. An index fund holds dozens or hundreds of companies, so a single company's failure doesn't wipe out your investment. If you're investing for retirement and have decades ahead, short-term declines are normal and usually recover over time.

Should I invest in one index fund or multiple?

A single total market index fund (like VTI or VTSAX) holds thousands of companies across all sectors and sizes, so it's diversified on its own. Many beginners start with one fund and add more later if they want to adjust their allocation — for example, adding a bond fund or international fund. There's no wrong answer; it depends on your goals and how much diversification you want.

What's the difference between an ETF and a mutual fund index fund?

Both track an index and hold many securities, but they trade differently. ETFs trade like stocks during market hours and can be bought and sold throughout the day. Mutual funds trade once per day after the market closes. For most long-term investors, the difference doesn't matter much; pick whichever your brokerage makes easiest to buy and hold.

Do I have to reinvest dividends?

Most brokerages let you choose. You can have dividends paid in cash, which you can then spend or reinvest manually, or you can set dividends to reinvest automatically, buying more shares of the fund. For long-term investing, automatic reinvestment is simpler and compounds your returns over time. You'll still owe taxes on the dividends in a taxable account, whether you reinvest or not.