You need a brokerage account, money to invest, and a decision about which index fund to buy
Investing in an index fund means buying shares of a fund that tracks a market index — a basket of stocks or bonds grouped by a rule. You cannot buy an index fund directly from the index itself. Instead, you open an account with a brokerage firm (a company licensed to buy and sell securities), deposit money, and place an order for the fund you want.
The process takes about 15 minutes to set up online, though the account may take one to three business days to fully set up. You will need a Social Security number, a bank account or debit card to fund it, and a decision about which index fund fits your goals — whether that is a total stock market fund, a bond fund, or something else.
Key Takeaways
- You must open an account with a brokerage firm such as Fidelity, Vanguard, or Charles Schwab before you can buy any index fund.
- The account setup is free at most brokerages, and you can start with as little as $1 to $500 depending on the firm and the specific fund.
- Index funds charge annual fees called expense ratios, which range from 0.03% to 0.20% for most low-cost index funds, and this fee is deducted automatically from your account.
- You place a buy order through the brokerage website or app, and the order executes at the end of the trading day at that day's closing price.
- Once you own shares, you can hold them indefinitely, add more money over time, or sell them whenever you want during market hours.
Choose a brokerage firm and open an account
A brokerage firm is the middleman that holds your money and executes your trades. Common firms include Fidelity, Vanguard, Charles Schwab, E*TRADE, and Robinhood. Each charges different fees and offers different tools, but all allow you to buy index funds. Most have no account opening fee and no minimum deposit requirement, though some index funds themselves have minimums (often $1,000 to $3,000 for the first purchase, though some start at $1).
Visit the brokerage website and click the button to open a new account. You will enter your name, address, Social Security number, and employment status. The firm will ask whether you want a taxable account (a regular investment account) or a retirement account such as an IRA. For most people starting out, a taxable account is simpler — you can withdraw money anytime without penalty, though you will owe taxes on gains when you sell.
After you submit the process, the firm verifies your identity, which usually takes a few minutes to a few hours. You will then link a bank account or provide a debit card number so you can transfer money in. This linking step may take one to three business days to complete.
Deposit money into your account
Once your account is active and linked to your bank, you can transfer money in. Most brokerages let you move money electronically (called an ACH transfer) from your checking or savings account at no cost. The transfer usually takes one to three business days to appear in your brokerage account.
You can deposit as much or as little as you want, and you can add money whenever you choose. There is no rule that says you must invest a lump sum all at once — many people deposit money monthly or whenever they have extra cash. The money sits in your account as cash until you place a buy order.
Decide which index fund to buy
An index fund tracks a specific market index. A total stock market index fund holds thousands of U.S. stocks weighted by size. A bond index fund holds government and corporate bonds. An international stock index fund holds stocks outside the U.S. Each fund has a different risk level and purpose.
Most brokerages let you search for funds by name or ticker symbol. If you want a total U.S. stock market fund, you might search for "VTSAX" (Vanguard's version), "FSKAX" (Fidelity's version), or "SWTSX" (Charles Schwab's version). Each tracks roughly the same index but is run by a different company. The fund's page will show you its expense ratio (the annual fee), its holdings, and its performance history.
If you are unsure which fund to choose, a total stock market index fund is a common starting point because it spreads your money across the entire U.S. stock market in one purchase. You can also hold multiple index funds in the same account — for example, 70% in a U.S. stock fund and 30% in a bond fund.
Place a buy order and confirm the purchase
Log into your brokerage account and search for the index fund you want to buy. Click on the fund name to open its detail page. Look for a button that says "Buy," "Invest," or "Trade" and click it.
You will see a form asking how many shares you want to buy or how much money you want to invest. Most brokerages let you choose either option — you can say "I want to spend $5,000" or "I want to buy 50 shares." If you choose the dollar amount, the system calculates how many shares that buys at the current price. Enter your choice and review the order summary.
The order will show you the fund name, the amount, and the estimated number of shares. It will also show the expense ratio so you know what annual fee you will pay. Click "Confirm" or "Place Order." The order executes at the end of the trading day (usually 4 p.m. Eastern time) at that day's closing price. You will receive a confirmation email with the details.
Understand what happens after you buy
Once your order executes, you own shares of the index fund. The shares appear in your account the next business day. You can see them listed by fund name, the number of shares you own, the price per share, and the total value.
The fund automatically reinvests any dividends it pays (usually quarterly) back into more shares of the same fund, unless you change this setting. The expense ratio is deducted automatically from the fund's value each year — you do not write a check or see a separate bill. It straightforward reduces the fund's daily price slightly.
You can hold the fund indefinitely, add more money to buy additional shares, or sell some or all of your shares whenever you want during market hours. If you sell at a profit, you will owe capital gains tax on the difference between what you paid and what you sold it for (this applies only in a taxable account, not in a retirement account).
Common mistakes to avoid
Do not wait for the "perfect" price to buy. Index funds are meant for long-term holding, and trying to time the market usually costs more than it saves. Buying regularly over time (called dollar-cost averaging) is a simpler approach than trying to guess when prices are lowest.
Do not confuse an index fund with a stock-picking service or a robo-advisor. An index fund is a passive investment — it straightforward holds the same stocks as the index it tracks. You are not paying a manager to pick winners; you are paying a small fee to hold a basket of securities automatically.
Do not ignore the expense ratio. A fund charging 0.50% per year costs five times more than one charging 0.10% per year. Over decades, that difference compounds significantly. Most index funds charge between 0.03% and 0.20% annually.
Frequently Asked Questions
What is the minimum amount I need to start investing in an index fund?
Most brokerages have no account minimum and no deposit minimum. However, individual index funds sometimes require a first purchase of $1,000 to $3,000, though many start at $1. After your first purchase, most funds let you add as little as $1 at a time. Check the specific fund's page on your brokerage website to see its minimum.
Can I buy an index fund through my employer's 401(k)?
Yes. Many 401(k) plans offer index funds as investment options. You choose the fund when you enroll in the plan, and your contributions are automatically invested in it. This is often simpler than opening a separate brokerage account, and contributions reduce your taxable income that year.
How long does it take to see returns on an index fund?
Index funds do not produce returns on a fixed schedule. The fund's value changes daily based on the prices of the stocks or bonds it holds. You see gains or losses when ready in your account balance, but index funds are designed for long-term holding — typically five years or more — because short-term price swings can be large.
Do I have to buy a whole share, or can I buy a fraction?
Most brokerages now allow fractional share purchases. If a fund costs $200 per share and you have $100 to invest, you can buy 0.5 shares. This makes it easier to invest small amounts or to invest a specific dollar amount rather than a specific number of shares.
What happens if the index fund closes or shuts down?
Index funds rarely close, but if one does, your brokerage automatically moves your shares to a similar fund or sells them and deposits the cash in your account. Your money is protected — the fund company cannot keep it. You may owe capital gains tax on the sale if you held the fund in a taxable account.