You need a brokerage account, then pick an index fund and place an order

Buying an index fund means opening an account at a brokerage firm, finding the specific fund you want to own, and placing a buy order. The whole process takes minutes once your account is funded. You do not need to pick individual stocks, time the market, or understand complex strategies — you are buying a basket of hundreds or thousands of stocks that track a published index like the S&P 500.

The real decision is not how to buy, but where to buy and which fund to choose. Different brokerages charge different fees, offer different funds, and have different minimum account balances. Some funds track the same index but cost more than others. This guide walks you through each step so you understand what you are choosing and why.

Key Takeaways

  • You must open a brokerage account with a firm like Fidelity, Vanguard, Charles Schwab, or a discount broker before you can buy any fund.
  • Index funds come in two main types — mutual funds and exchange-traded funds (ETFs) — and both track an index, but they trade and settle differently.
  • The fund's expense ratio (annual cost) varies widely even for funds tracking the same index, so comparing costs before you buy saves money over years.
  • You can buy most index funds with no minimum investment at major brokerages, though some mutual funds still require $1,000 or $3,000 to start.
  • Once you place an order, mutual funds settle the next business day while ETFs settle like stocks, usually the same day or next day depending on when you trade.

Choose a brokerage and open an account

A brokerage is the firm that holds your money and executes your trades. You cannot buy an index fund without one. The major brokerages used by individual investors are Fidelity, Vanguard, Charles Schwab, E-Trade, and Merrill Edge. Discount brokerages like Robinhood, Webull, and M1 Finance also offer index funds, usually with lower or no account minimums.

Opening an account takes 10 to 15 minutes online. You will provide your name, Social Security number, address, employment status, and banking information. The brokerage will ask what type of account you want — a taxable brokerage account (for money you have already paid taxes on), a traditional IRA (tax-deferred retirement savings), or a Roth IRA (tax-free retirement savings). If you are unsure, a taxable brokerage account is the simplest starting point. You will then link a bank account or transfer money to fund your brokerage account.

Some brokerages require a minimum deposit to open an account; others do not. Vanguard and Fidelity historically required $1,000 to $3,000 minimums, but many have lowered or eliminated these. Check the specific brokerage's website for current requirements. Once your account is open and funded, you are ready to search for and buy a fund.

Understand the difference between mutual funds and ETFs

Both mutual funds and ETFs are index funds — they both track an index and hold the same underlying stocks. The difference is how they trade and settle. A mutual fund is priced once per day, after the market closes. You place an order during the day, but it executes at that day's closing price, which you do not know until after 4 p.m. Eastern. Settlement happens the next business day.

An exchange-traded fund (ETF) trades like a stock throughout the day. You can see the price in real time, place an order at any time the market is open, and the price you see is the price you pay. Settlement is usually the next business day, though some brokerages offer same-day settlement. ETFs also tend to have lower expense ratios than mutual funds tracking the same index.

For a beginner, ETFs are often simpler because you see the price before you buy and you can trade during market hours. Mutual funds work fine too, but the one-price-per-day model confuses some people. Both are legitimate choices — pick whichever feels clearer to you.

Compare expense ratios across funds tracking the same index

Multiple funds can track the S&P 500, the total U.S. stock market, or any other index. They all hold roughly the same stocks, but they charge different annual fees called expense ratios. An expense ratio of 0.03% means you pay $3 per year for every $10,000 invested. An expense ratio of 0.50% means you pay $50 per year on the same $10,000.

The difference sounds small, but it compounds. Over 30 years, a 0.47% difference in expense ratio can cost you tens of thousands of dollars in lost growth. Vanguard's S&P 500 ETF (VOO) charges 0.03%. Fidelity's equivalent (FXAIX) also charges 0.03%. Some funds charge 0.10% or higher for the same index. Before you buy, search your brokerage's fund screener or look up the fund's fact sheet to find the expense ratio. Choose the lowest-cost option for the index you want.

You can find expense ratios on the fund company's website, on financial sites like Morningstar or Yahoo Finance, or in your brokerage's fund search tool. Write down the ticker symbol (like VOO or FXAIX) and the expense ratio, then compare across the funds your brokerage offers.

Search for the fund in your brokerage and place an order

Log into your brokerage account and look for a "Buy" or "Trade" button. Enter the fund's ticker symbol — for example, VOO for Vanguard's S&P 500 ETF, or FSKAX for Fidelity's total stock market mutual fund. The brokerage will show you the fund's current price (if it is an ETF) or the previous day's closing price (if it is a mutual fund).

Decide how much money you want to invest. You can buy a set dollar amount (for example, $500) or a set number of shares. For a beginner, buying a dollar amount is simpler — you enter $500 and the brokerage calculates how many shares that buys. For ETFs, you can only buy whole shares unless your brokerage offers fractional shares, which most now do. For mutual funds, you can buy any dollar amount.

Review the order summary to confirm the fund name, the amount, and the estimated cost. Then click "Confirm" or "Place Order." For a mutual fund, the order executes at that day's closing price. For an ETF, the order executes at the price shown (or close to it if the price moves while you are placing the order). You will receive a confirmation email with your order number and the final price.

Monitor your purchase and understand what happens next

After you place an order, the fund appears in your account within one to two business days. You will see the number of shares you own and the current value. The value will change every day the market is open, based on the index the fund tracks. This is normal and expected. You do not need to do anything — the fund automatically rebalances itself to stay aligned with the index.

If you want to buy more of the same fund later, you can place another order the same way. If you want to sell, you use the "Sell" button and follow the same process in reverse. Most brokerages let you set up automatic monthly or quarterly investments, which is useful if you want to invest a fixed amount regularly without having to log in each time.

Keep your brokerage login and password find. You will use this account to check your balance, place trades, and eventually withdraw money. Some brokerages offer two-factor authentication — use it if available. Your brokerage is required by law to protect your account, but you are responsible for keeping your login credentials safe.

Account types and tax implications

The type of account you chose when you opened your brokerage affects how you pay taxes on your gains. In a taxable brokerage account, you pay capital gains tax on any profit when you sell the fund. You also pay tax on any dividends the fund distributes. This happens every year, even if you do not sell.

In a traditional IRA, you do not pay tax on gains or dividends while the money is in the account. You pay tax when you withdraw money in retirement. In a Roth IRA, you do not pay tax on gains, dividends, or withdrawals — ever. However, IRAs have annual contribution limits (currently $7,000 per year for people under 50) and rules about when you can withdraw without penalty.

For your first index fund purchase, a taxable brokerage account is the simplest. You can invest any amount, withdraw anytime, and there are no contribution limits. If you have a workplace retirement plan or are saving specifically for retirement, an IRA may make more sense. Talk to a tax professional if you are unsure which account type fits your situation.

Frequently Asked Questions

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

No. Most brokerages have no minimum deposit to open an account, and you can buy index funds with as little as $1 to $100 depending on the fund's price. Some mutual funds still require $1,000 or $3,000 minimums, but ETFs and many mutual funds have no minimum. Check your chosen brokerage's website for current requirements.

Can I buy index funds through my bank?

Some banks offer brokerage services, but most people find dedicated brokerages like Fidelity or Vanguard easier to use and cheaper. Banks often charge higher fees and have fewer fund options. If your bank offers brokerage services, compare their expense ratios and fees to a dedicated brokerage before deciding.

What happens if the brokerage goes out of business?

Your account is protected by the Securities Investor Protection Corporation (SIPC), which covers up to $500,000 per account if a brokerage fails. Your index funds themselves are your property — they do not disappear. In practice, a failing brokerage is usually acquired by another firm that transfers all customer accounts intact.

Should I buy one index fund or multiple ones?

A single total market index fund (like one tracking the entire U.S. stock market) is enough to start. Some people buy multiple funds to diversify across U.S. stocks, international stocks, and bonds, but one fund is a solid beginning. Start straightforward and add complexity only if you have a specific reason.

Can I set up automatic investments after I buy the first fund?

Yes. Most brokerages let you set up automatic monthly or quarterly transfers from your bank account to buy a specific fund. This is called dollar-cost averaging and removes the need to remember to invest each month. Set it up in your account settings once your first purchase is complete.