How to Invest in Index Funds: A Step-by-Step Guide for Beginners

An index fund buys every stock in a market index, such as the S&P 500, so you own a small piece of hundreds of companies in a single purchase. Nobody picks stocks, which keeps the fees low. For most beginners it's the simplest way to start investing.

Checked October 12, 2026. Fund fees and fund lineups change; confirm on the provider's site before you buy.

What Warren Buffett recommends

Warren Buffett has long told ordinary investors to use a low-cost S&P 500 index fund. In his 2013 letter to Berkshire Hathaway shareholders, he wrote that the instructions for the money he's leaving his wife are to put 90% in a very low-cost S&P 500 index fund (he suggested Vanguard's) and 10% in short-term government bonds. He also won a 10-year bet, from 2008 through 2017, that an S&P 500 index fund would beat a group of hedge funds after fees.

Step 1: Pick the account

The fund sits inside an account. Which account you use decides how it's taxed.

• 401(k) at work. Start here if your employer matches contributions. Most plans offer at least one S&P 500 or target-date index fund.
• Roth IRA. You invest money you've already paid tax on, and withdrawals in retirement are tax-free. See how to open a Roth IRA.
• Regular brokerage account. No limits and you can withdraw anytime, but you pay tax on dividends and gains each year you have them.

Step 2: Pick the index

• S&P 500: about 500 of the largest US companies. The most common starting point.
• Total US stock market: the S&P 500 plus thousands of mid-size and small companies. Performance is very close to the S&P 500.
• Total international: companies outside the US. Often added as a second fund.
• Total bond market: lower risk and lower expected return. Usually a bigger share of the portfolio as you get closer to needing the money.

New to these names? Dow vs. S&P 500 vs. Nasdaq explains the differences.

Step 3: Compare the fees

Funds that track the same index hold nearly the same stocks, so the fee (the expense ratio) is the main difference. A 0.03% expense ratio costs $3 a year for every $10,000 invested.

FZROX can only be held at Fidelity; read our FZROX review for the trade-offs. To compare the ETFs, see VOO vs. VTI vs. QQQ.

Step 4: Choose ETF or mutual fund

• ETFs trade like stocks during the day and can be bought at any broker. Most brokers let you buy fractional shares for as little as $1.
• Index mutual funds trade once a day at the closing price and make automatic monthly investing easy, but they're usually cheapest at the company that runs them.

More detail: ETF vs. mutual fund.

Step 5: Buy your first shares

1. Open and fund the account (a bank transfer usually takes 1 to 3 business days).
2. Search for the fund's ticker, for example VOO or FXAIX.
3. Enter a dollar amount. For ETFs, a market order during trading hours is fine for a fund this large.
4. Turn on dividend reinvestment.
5. Set up an automatic monthly investment. Investing the same amount on a schedule is called dollar-cost averaging.

Types of index funds

Example: buying FXAIX in a Roth IRA at Fidelity

1. Open a Roth IRA online (about 10 minutes; you'll need your Social Security number and bank details).
2. Transfer money in. You can contribute up to the yearly IRA limit if your income is under the Roth limits.
3. Once the transfer settles, choose Trade, search FXAIX and enter the dollar amount. Mutual fund orders fill at that day's closing price.
4. Choose to reinvest dividends and capital gains.
5. Set up automatic investments so a fixed amount moves from your bank and buys FXAIX every month.

The steps are almost the same at Schwab (with SWPPX) or Vanguard (with VOO).

Index funds vs. robo-advisors

A robo-advisor like Betterment or Wealthfront builds and rebalances a portfolio of index funds for you, usually for about 0.25% of your balance a year on top of the funds' own fees. That's $25 a year per $10,000. It can be worth it if you'd otherwise never rebalance or want automatic tax-loss harvesting. If you're happy with one target-date fund, you're already getting most of the benefit for free. Compare them in Wealthfront vs. Betterment.

Index funds in your 401(k)

• Look for the cheapest index option in your plan's fund list. Its expense ratio should be well under 0.20%.
• Don't mix a target-date fund with other funds unless you mean to; the target-date fund is already a full portfolio.
• Limit company stock. Holding a lot of your employer's shares ties your savings to the same company as your paycheck.

When it makes sense to sell

• You need the money for the goal you saved for.
• You're rebalancing back to your target mix.
• You're moving to a cheaper fund that tracks the same index (in a taxable account, check the tax cost first).
• You're harvesting a loss in a taxable account.

A scary headline or a falling market isn't, on its own, a reason to sell. See how to survive a market crash.

Common mistakes

• Owning several funds that track the same thing. An S&P 500 fund plus a total-market fund is mostly the same stocks twice.
• Leaving cash uninvested. Money transferred into an IRA sits as cash until you buy the fund.
• Selling in a downturn. Index funds fall with the market. They work best when held for years.

To see what regular contributions can grow to, try the compound interest calculator.

Why index funds beat most stock pickers

Most professionally managed funds that try to beat the market don't, once fees are included. S&P's long-running SPIVA reports have found that roughly 9 in 10 actively managed US large-company funds trailed the S&P 500 over 15-year periods. An index fund doesn't try to beat the market. It matches it, minus a very small fee, and over long periods that has put it ahead of most of the funds trying to do better.

How much fees cost you

Here's $10,000 left to grow for 30 years at a 7% yearly return before fees:

The fee comes out every year whether the fund does well or not, so a small difference compounds into a large one.

What regular investing could grow to

Investing $300 a month for 30 years, with a 7% average yearly return, would grow to about $366,000. You'd have put in $108,000; the rest is growth. Returns are never this smooth in real life, and some years will be negative. Try your own numbers in the compound interest calculator.

Simple portfolios you can copy

The exact percentages matter less than picking a mix you'll stick with in a downturn. See the 60/40 portfolio and how to rebalance.

Where to buy

Any of these is a good home for index funds. Compare more in Fidelity vs. Vanguard and best investment apps.

How index funds are taxed

• Inside a 401(k) or IRA: no tax on dividends or gains while the money stays in the account.
• In a regular brokerage account: dividends are taxed in the year you get them, and you pay capital gains tax when you sell at a profit. Holding for over a year gets the lower long-term rate (see the one-year rule).
• ETFs are usually more tax-efficient than mutual funds, because they rarely pass taxable gains on to you.

FAQ

How much money do I need to start? At most brokers, $1 for an ETF bought as fractional shares. Fidelity and Schwab index mutual funds have no minimum; Vanguard's Admiral mutual funds require $3,000.

Are index funds safe? They spread your money across many companies, so one company failing won't sink you. They still rise and fall with the market and can lose value for years at a time.

Which is better, an S&P 500 fund or a total-market fund? Either works as a core holding. Their returns have been very close over long periods.

Do index funds pay dividends? Yes. Stock index funds pass along the dividends of the companies they hold, usually quarterly. You can reinvest them automatically.

What is a target-date fund? A single fund that holds a mix of stock and bond index funds and gradually shifts toward bonds as its target year approaches. It's the simplest one-fund option, usually in a 401(k).

Can I lose all my money in an index fund? A broad stock index fund would only go to zero if every company in it failed. It can still lose a large share of its value in a crash, as the S&P 500 did in 2008 and 2020, before recovering.

How often should I check my index funds? Once a month or less is plenty. Checking daily makes it more tempting to sell during drops.

Should I invest a lump sum or spread it out? Investing it all at once has historically come out ahead more often, but spreading it over a few months can make a big amount easier to commit. See DCA vs. lump sum.

Can I buy index funds for my kids? Yes, through a custodial account (UGMA/UTMA), a 529 college savings plan, or a custodial Roth IRA if your child has earned income.

Do index funds have minimums? ETFs have no minimum beyond the price of one share, or $1 with fractional shares. Fidelity and Schwab index mutual funds have no minimum; Vanguard's Admiral funds need $3,000.