What an index fund is and how to start one

An index fund is a collection of stocks or bonds that mirrors a specific market index — a pre-set list of companies or securities. The most common example is the S&P 500, which tracks 500 large U.S. companies. When you buy shares in an index fund, you own a small piece of all those companies at once, rather than picking individual stocks yourself.

To start, you open an account with a brokerage firm — the company that holds your money and executes trades. You then deposit cash into that account and use it to purchase index fund shares. The fund itself does the work of holding all the underlying stocks and rebalancing them when the index changes. You pay a small annual fee (called an expense ratio) to cover the fund's operating costs, typically between 0.03% and 0.20% per year for index funds.

The process takes about 15 minutes to set up online, though your first deposit may take 3 to 5 business days to clear depending on your bank.

Key Takeaways

  • You need a brokerage account with a firm like Vanguard, Fidelity, or Charles Schwab before you can buy any index fund shares.
  • Index funds charge annual fees (expense ratios) that range from 0.03% to 0.20%, and lower-cost funds are available from most major brokerages.
  • Your initial deposit must clear your bank, which typically takes 3 to 5 business days, before you can purchase shares.
  • Index funds are designed to track a specific market index and require no active stock-picking on your part once you buy in.
  • You can set up automatic monthly deposits to build your position over time, a strategy called dollar-cost averaging.

Choosing a brokerage and opening an account

The brokerage you choose matters mainly for fees, user interface, and customer service. Major brokerages like Vanguard, Fidelity, Charles Schwab, and E*TRADE all offer low-cost index funds and charge no commission to buy or sell them. Smaller or newer brokerages may offer lower minimum deposits or simpler interfaces, but verify their fee structure before opening an account.

To open an account, visit the brokerage's website and select "Open an Account" or similar. You will provide your name, address, Social Security number, employment status, and bank details. The brokerage will verify your identity — this usually happens instantly online, though some firms mail a confirmation code. Once approved, you can log in and link a bank account for deposits.

Most brokerages offer two main account types: a taxable brokerage account (for any amount, with annual tax reporting) and a retirement account like an IRA (with contribution limits and tax advantages). If you are saving for retirement, an IRA is usually the better choice. If you are saving for a non-retirement goal, use a taxable account.

Depositing money and making your first purchase

After your account is open, link your bank account to the brokerage. You can then transfer money from your bank to your brokerage account. This transfer typically takes 3 to 5 business days to complete, though some brokerages offer next-day transfers for a small fee or through their mobile app.

Once the money arrives in your brokerage account, you can purchase index fund shares. Log into your account, search for the index fund by its ticker symbol (for example, VOO for Vanguard's S&P 500 fund, or FSKAX for Fidelity's equivalent), and enter the dollar amount or number of shares you want to buy. The purchase executes immediately during market hours (9:30 a.m. to 4 p.m. Eastern Time on weekdays), and you will see the shares in your account within minutes.

If you place an order after market hours or on a weekend, it will execute at the next market open. You will pay the fund's current share price, which changes daily based on the underlying stocks' values.

Understanding fees and expense ratios

Index funds charge an annual fee called an expense ratio, expressed as a percentage of your investment. A 0.05% expense ratio on a $10,000 investment costs $5 per year. This fee is deducted automatically from your fund's value and is not a separate bill.

Different index funds tracking the same index may have different expense ratios. Vanguard's S&P 500 fund (VOO) charges 0.03% annually, while Fidelity's version (FSKAX) charges 0.015%. Over decades, even small differences compound significantly. A 0.05% difference on $100,000 costs $50 per year, or $5,000 over 100 years before accounting for investment growth.

Most major brokerages do not charge commissions to buy or sell index funds, and many offer commission-free trading on their own house-brand funds. Always check the fund's prospectus or fact sheet for the exact expense ratio before purchasing.

Deciding how much to invest and how often

There is no minimum investment required to start, though some brokerages set minimums of $500 to $1,000 for certain accounts. You can begin with any amount you can afford and add to it over time.

Many investors use dollar-cost averaging: investing a fixed amount at regular intervals (for example, $500 per month) rather than trying to time the market. This approach removes the pressure to guess when prices are lowest and builds discipline into your savings. Most brokerages allow you to set up automatic monthly transfers and purchases.

How much you invest depends on your financial situation. A common guideline is to invest money you will not need for at least 5 years, since stock markets fluctuate in the short term. If you have high-interest debt (credit cards, personal loans), paying that down first usually makes more financial sense than investing.

Tax considerations for different account types

In a taxable brokerage account, you pay taxes on dividends and capital gains each year, even if you do not sell shares. Index funds typically generate lower taxes than actively managed funds because they trade less frequently, but you still owe taxes on gains.

In a traditional IRA, contributions may be tax-deductible, and you pay no taxes on gains until you withdraw money in retirement. In a Roth IRA, contributions are not deductible, but withdrawals in retirement are tax-free. Both have annual contribution limits ($7,000 in 2024 for most people under 50) and rules about when you can withdraw without penalty.

If you are self-employed or own a small business, a SEP IRA or Solo 401(k) may allow larger contributions. Consult a tax professional or use your brokerage's educational resources to determine which account type fits your situation.

Monitoring your investment and rebalancing

After you buy index fund shares, you do not need to do anything. The fund automatically holds all the underlying stocks and rebalances them when the index changes. You do not pick individual stocks, time the market, or make frequent trades.

Check your account balance quarterly or annually to confirm your deposits are going through and your balance is growing. Avoid the temptation to sell during market downturns — index funds are designed for long-term holding, and selling low locks in losses.

If you have multiple investments (for example, stocks and bonds in different accounts), you may want to rebalance once a year to maintain your target mix. Most brokerages offer tools or calculators to help with this. If you are investing primarily in index funds within a single account, rebalancing is usually unnecessary.

Frequently Asked Questions

Can I lose money in an index fund?

Yes. Index funds track the market, so if the market declines, your investment value declines too. However, markets have historically recovered from downturns over 5+ year periods. Index funds are less risky than individual stocks because they spread your money across many companies, but they are not risk-free.

What is the difference between an index fund and an ETF?

Both track an index, but ETFs (exchange-traded funds) trade like stocks throughout the day, while mutual fund index funds trade once daily after market close. ETFs often have lower expense ratios and may be more tax-efficient. For most investors, the difference is small; choose whichever your brokerage makes easiest to buy.

Do I need a lot of money to start?

No. Most brokerages allow you to open an account with $0 and buy your first shares with any amount. Some funds have $1 minimums per purchase. Start with what you can afford and add regularly over time.

Should I invest in a single index fund or multiple ones?

A single broad-market index fund (like the S&P 500) is enough for most investors. Some people add a bond index fund for stability or an international stock index fund for diversification. Avoid owning multiple funds that track the same index, as this creates unnecessary overlap.

What happens to my index fund shares if the brokerage goes out of business?

Your shares are protected by SIPC (Securities Investor Protection Corporation) up to $500,000 per account. This means your shares belong to you, not the brokerage, and would transfer to another firm if your brokerage failed. Choose a well-established brokerage to minimize this risk.