If you have ever been told to just buy an S&P 500 index fund, there is a very good chance someone meant the Vanguard 500 Index Fund. It is one of the oldest, largest, and cheapest ways to own a piece of the U.S. stock market in a single purchase.
Vanguard offers it in two forms with the same engine inside: VFIAX, a mutual fund, and VOO, an exchange-traded fund. Here is what the fund actually holds, what it costs to own, and how to buy it.
What the Vanguard 500 Index Fund Holds
The fund tracks the S&P 500, an index of about 500 of the largest publicly traded U.S. companies. When you buy a share, you own a tiny slice of all of them at once.
The biggest positions are the largest companies by market value, names like Apple, Microsoft, and Amazon. Because the index is weighted by size, those giant companies make up a larger share of the fund than smaller members.
That gives you instant diversification across sectors like technology, healthcare, finance, and consumer goods, all in one holding. You are not betting on a single stock. You are betting on the broad U.S. market.
VFIAX vs VOO: Same Index, Different Wrapper
VFIAX and VOO track the exact same index and hold the same stocks. The difference is structure and how you trade them.
VFIAX is a mutual fund. It usually carries a 3,000 dollar minimum investment and prices once a day, after the market closes. VOO is the ETF version. It has no opening minimum beyond the price of one share, and it trades live throughout the day like a stock.
The Expense Ratio: Why Low Cost Matters
The expense ratio is the annual fee the fund charges, expressed as a percentage of your investment. It comes out automatically, so you never write a check, but it quietly affects your returns every year.
As of 2026, VOO carries an expense ratio of about 0.03 percent, and VFIAX is about 0.04 percent. On a 10,000 dollar investment, 0.03 percent is roughly 3 dollars a year.
That is strikingly low. Many actively managed funds charge 0.50 percent to 1.00 percent or more, and over decades that gap can cost you tens of thousands of dollars in lost compounding. Low fees are one of the main reasons index funds like this one are so widely recommended.
How to Buy the Vanguard 500 Index Fund
You have two main paths, and they depend on which version you want.
To buy VFIAX, the mutual fund, you generally open a Vanguard account, or use a workplace 401(k) that offers it. Expect the 3,000 dollar minimum and end-of-day pricing.
To buy VOO, the ETF, you can use almost any U.S. brokerage. The ETF trades like any stock, so if a platform lets you buy shares of Apple, it almost certainly lets you buy VOO, often with fractional shares so you can start with a few dollars.
One brokerage where you can buy VOO is Robinhood, which offers commission-free trading and fractional shares, so you can own a slice of the S&P 500 even if a full share costs more than you want to spend today.
Robinhood
Robinhood
Robinhood is a trading platform that brings stocks, ETFs, options, futures, prediction markets, crypto, and retirement accounts together in one app.
Standout feature
One platform for stocks, ETFs, options, futures, prediction markets, and crypto
Fees
$0 commission on stocks, ETFs, and options.
Pros
Zero-commission trading on stocks, ETFs, and options
Cons
Best perks (high APY, lower margin rates) require Gold subscription ($5/month)
Worth being clear here: these brokerages are simply places to buy an S&P 500 ETF like VOO. You can also buy directly from Vanguard, and for the VFIAX mutual fund a Vanguard account is usually the most direct route. The partners below are convenient options, not the only ones.
Another brokerage that offers commission-free access to ETFs like VOO is Public, which pairs fractional investing with a clean app and educational features that can help newer investors understand what they own.
Public
Public
Investing for those who take it seriously. Invest in stocks, bonds, options, crypto & more.
Standout feature
A 5%+ yield Bond Account paired with 3.3% APY on cash — Public is one of the only consumer apps where idle and conservative money is treated as seriously as the equity portfolio.
Fees
Free
Pros
• Invest in stocks, bonds, crypto & more• Earn 3.3% APY* on your cash with no fees• 1% match when you transfer your portfolio• Lock in a 5%+ yield with a Bond Account
Cons
Customer support is in-app and email only, no phone
Who the Fund Suits
The Vanguard 500 Index Fund fits long-term investors who want broad U.S. market exposure without picking individual stocks. It is a common core holding in retirement accounts because of its diversification and rock-bottom cost.
It is less suited to anyone who needs the money in the next year or two. Stocks rise and fall, and the S&P 500 can drop sharply in a bad year. Money you may need soon usually belongs somewhere more stable, like a savings account.
Keep in mind that VFIAX and VOO only track large U.S. companies. They do not include small companies, bonds, or international stocks, so many investors pair the fund with other holdings for a fuller portfolio.
VFIAX or VOO: Which Should You Pick?
Long-term returns between the two are very close, since they hold the same stocks. The choice usually comes down to how you like to invest.
If you want to start with a small amount, buy fractional shares, and trade during the day, the VOO ETF is the flexible pick. If you prefer automatic, set-it-and-forget-it mutual fund investing inside a Vanguard account and can meet the minimum, VFIAX works well.
Either way, you are buying the same basket of America's biggest companies at one of the lowest costs in investing. All investing involves risk, including possible loss of principal.
Frequently Asked Questions
What is the difference between VFIAX and VOO?
They track the same S&P 500 index and hold the same stocks. VFIAX is a mutual fund with a roughly 3,000 dollar minimum that prices once a day. VOO is an ETF with no minimum beyond one share's price and trades live throughout the day. Long-term returns are very similar.
What is the expense ratio of the Vanguard 500 Index Fund?
As of 2026, VOO is about 0.03 percent and VFIAX is about 0.04 percent per year. That means roughly 3 to 4 dollars annually per 10,000 dollars invested, which is far lower than most actively managed funds.
How do I buy the Vanguard 500 Index Fund?
For VFIAX, you typically open a Vanguard account or use a 401(k) that offers it. For the VOO ETF, you can use almost any brokerage, including Vanguard or third-party platforms, and often buy fractional shares to start small.
Is the Vanguard 500 Index Fund a good investment for beginners?
Many consider it a solid core holding because it offers broad diversification at very low cost. It is best suited to long-term goals, since stocks can fall in the short term. It only covers large U.S. companies, so some investors add bonds or international funds. This is educational information, not personalized advice.
