You can invest in index funds through a brokerage account, retirement account, or robo-advisor platform
The most direct route is to open a brokerage account with a firm that offers index funds — Vanguard, Fidelity, Charles Schwab, and Merrill Edge are common choices. You fund the account with your own money, then buy index fund shares the same way you would buy individual stocks. The fund holds a basket of securities that track a market index, so you own a piece of many companies at once rather than betting on single stocks.
If you have earned income, a retirement account — a 401(k) through your employer or an IRA that you open yourself — often gives you tax advantages that a regular brokerage account does not. Many employer 401(k) plans offer index fund options alongside other investments. An IRA lets you choose any brokerage and any index funds they carry. Both routes let you invest pre-tax money (in a traditional account) or after-tax money that grows tax-free (in a Roth account).
A third option is a robo-advisor platform like Betterment or Wealthfront, which automates the process by building a portfolio of index funds based on your age and risk tolerance, then rebalancing it automatically. These platforms charge a small annual fee — typically 0.25% to 0.50% of your account balance — for this automation.
Key Takeaways
- Open a brokerage account, retirement account, or robo-advisor platform, then deposit money and purchase index fund shares using that money.
- A 401(k) or IRA offers tax advantages that a regular brokerage account does not, but requires earned income or access to an employer plan.
- Index funds charge lower fees than actively managed funds because they simply track an index rather than paying a manager to pick stocks.
- You can start with small amounts — many brokerages allow purchases of fractional shares, so you do not need thousands of dollars upfront.
- The fund itself handles buying and selling the underlying securities; you only decide which fund to buy and how much money to invest.
Opening a brokerage account and choosing a platform
A brokerage account is a regular investment account held in your name. You open one by visiting a brokerage website, providing your name, address, Social Security number, and employment information, then linking a bank account or depositing money. The brokerage verifies your identity and approves the account, usually within one to three business days.
Different brokerages offer different index funds and charge different fees. Vanguard, Fidelity, and Charles Schwab each have their own index funds and also carry index funds from other providers. Some brokerages charge a commission per trade; others offer commission-free trading. Most major brokerages now allow you to buy fractional shares, meaning you can invest $50 and own a piece of an index fund even if one full share costs more.
Once your account is open and funded, you search for the index fund you want — by name or ticker symbol — and place a buy order. The order executes at the next market close (usually 4 p.m. Eastern time on weekdays). You then own shares of that fund, and the fund's value changes daily as the underlying securities move.
Using a 401(k) or IRA for tax-advantaged investing
A 401(k) is an employer-sponsored retirement plan. If your employer offers one, you enroll through your company's benefits portal and choose how much to contribute from each paycheck — the money comes out pre-tax, reducing your taxable income that year. Your employer may also match a portion of your contributions. The 401(k) plan offers a menu of investment options, which usually includes several index funds.
An IRA (Individual Retirement Account) is a retirement account you open yourself, not through an employer. You can open one at any brokerage. A traditional IRA lets you deduct contributions from your taxes in the year you make them (subject to income limits if you also have a 401(k)). A Roth IRA does not give you an immediate tax deduction, but the money grows tax-free and you can withdraw it tax-free in retirement. Both types allow you to invest in any index funds the brokerage carries.
Contribution limits change yearly. For 2024, you can contribute up to $7,000 to an IRA (or $8,000 if you are 50 or older) and up to $23,500 to a 401(k) (or $31,000 if you are 50 or older). Money in these accounts cannot be withdrawn before age 59½ without penalty, with limited exceptions. The tax advantages make these accounts powerful tools for long-term investing.
Understanding index fund fees and how they affect returns
Every index fund charges a fee called an expense ratio, expressed as a percentage of your investment per year. A fund with a 0.05% expense ratio costs $5 per year on a $10,000 investment. A fund with a 1% expense ratio costs $100 on the same investment. Over decades, this difference compounds — a 0.05% fund will significantly outpace a 1% fund even if both track the same index.
Index funds typically charge lower fees than actively managed funds because they simply hold the securities in an index rather than paying a manager to research and pick stocks. Vanguard, Fidelity, and Charles Schwab all offer index funds with expense ratios below 0.10%. Some brokerages also charge trading commissions or account fees, though most major brokerages have eliminated these for index funds.
When comparing index funds, look at the expense ratio first. Two funds tracking the same index should perform nearly identically, so the lower-cost option is usually the better choice. The fund's prospectus or fact sheet lists the expense ratio clearly.
Deciding how much to invest and how often
You can start investing with any amount you have available. Many brokerages allow fractional share purchases, so you can invest $10, $100, or $1,000 — there is no minimum. Some brokerages set a minimum account balance (often $0 to $500), but this is the initial deposit, not a per-trade minimum.
A common strategy is to invest a fixed amount on a regular schedule — $200 per month, for example, or $500 every quarter. This is called dollar-cost averaging. You buy more shares when prices are low and fewer when prices are high, which can reduce the impact of market timing mistakes. You can set up automatic transfers from your bank account to your investment account, then manually buy the index fund, or use a robo-advisor to automate both steps.
Another approach is to invest a lump sum when you have it — a tax refund, a bonus, an inheritance. The timing does not matter much over long periods; what matters is that you invest consistently and leave the money alone.
What happens after you buy index fund shares
Once you own index fund shares, you do not need to do anything. The fund manager automatically buys and sells the underlying securities to track the index. You receive statements showing your account balance and the value of your shares. The fund may pay dividends (distributions of company earnings), which you can reinvest automatically or take as cash.
Your account value changes daily as the index moves. You can check it anytime through your brokerage's website or app. You can buy more shares whenever you want, or sell shares if you need the money. Selling triggers a taxable event — you owe capital gains tax on any profit — so in a regular brokerage account, it is usually better to hold long-term. In a retirement account, you can buy and sell without tax consequences until you withdraw money in retirement.
Rebalancing — adjusting your mix of different index funds to maintain your target allocation — is optional but common. If you own a U.S. stock index fund and an international stock index fund in a 70/30 split, market movements might shift that to 75/25 over time. You can rebalance by buying more of the underweight fund or selling some of the overweight fund. Robo-advisors do this automatically; with a regular brokerage account, you decide when and how often to rebalance.
Comparing index funds that track the same market
Multiple index funds can track the same index. The S&P 500 index, for example, is tracked by Vanguard's VOO, Fidelity's FXAIX, Schwab's SWPPX, and many others. All of these funds hold roughly the same 500 stocks in roughly the same proportions, so their performance is nearly identical. The main differences are expense ratio, minimum investment, and which brokerage offers them.
| Fund Name | Ticker | Expense Ratio | Best For |
|---|---|---|---|
| Vanguard S&P 500 ETF | VOO | 0.03% | Any brokerage; very low cost |
| Fidelity S&P 500 Index Fund | FXAIX | 0.015% | Fidelity accounts; lowest cost |
| Schwab S&P 500 Index Fund | SWPPX | 0.03% | Schwab accounts; no minimum |
If you open an account at Fidelity, FXAIX is usually the best choice for S&P 500 exposure because it has the lowest expense ratio. If you use a different brokerage, VOO is widely available and costs nearly as little. The difference between 0.015% and 0.03% is small in dollar terms — $1.50 versus $3 per year on a $10,000 investment — but compounds over decades.
Frequently Asked Questions
Do I need a lot of money to start investing in index funds?
No. Most brokerages allow fractional share purchases and have no minimum investment. You can start with $10 or $50. Some brokerages set a minimum account balance of $0 to $500 for the initial deposit, but this is a one-time requirement, not a per-trade minimum. After that, you can invest any amount you choose.
Can I lose money investing in index funds?
Yes. Index funds track market indexes, and markets fluctuate. If you buy an S&P 500 index fund and the market drops 20%, your investment drops 20% too. Over long periods (10+ years), stock market indexes have historically recovered from downturns, but short-term losses are possible. Bond index funds are less volatile but still carry risk.
Should I invest in a 401(k) or a regular brokerage account?
If your employer offers a 401(k) with a match, contribute enough to capture the full match — that is assistance programs. After that, a Roth IRA is often a good next step because it offers tax-free growth and more investment choices. A regular brokerage account makes sense once you have maxed out retirement account contributions or if you need access to the money before age 59½.
How often should I buy index fund shares?
That depends on your situation. If you receive a regular paycheck, monthly or bi-weekly contributions work well. If you have a lump sum, you can invest it all at once. The timing of individual purchases matters less than investing consistently over time. Automatic monthly investments are simpler than trying to time the market.
What is the difference between an index fund and an ETF?
An ETF (exchange-traded fund) is a type of index fund that trades like a stock — you buy and sell it during market hours at a price that changes throughout the day. A traditional index fund (mutual fund) trades once per day at the closing price. Both can track the same index and have similar costs. ETFs are often slightly cheaper and more tax-efficient, but the difference is small for most investors.