Vanguard runs two of the most popular S&P 500 index funds in the country. VFIAX is the mutual fund version, and VOO is the ETF version. Both track the same index, but they trade and price differently.
This guide breaks down what each fund does, how the fees and minimums compare, and how to buy them through a broker like Robinhood. Vanguard built its reputation on low costs, and these two funds are core to that story.
Why Vanguard Is Tied to Index Investing
Vanguard launched the first index mutual fund for everyday investors back in 1976, under founder Jack Bogle. The idea was simple. Rather than try to pick winning stocks, the fund would hold every stock in a major index and keep fees as low as possible.
That idea grew into a giant business. Vanguard now manages trillions of dollars and has helped pull industry-wide fees down to a fraction of what they used to be.
VFIAX, the Mutual Fund Version
VFIAX is the Vanguard 500 Index Fund Admiral Shares. It is a mutual fund that holds the same 500 stocks as the S&P 500.
How VFIAX Trades
A mutual fund only prices once per day. You place an order during the day, and your buy or sell happens at the closing price. You cannot trade VFIAX intraday like a stock.
Minimum Investment
VFIAX requires a 3,000 dollar minimum to start. After that, you can add any dollar amount you want. The expense ratio is very low, around 0.04 percent per year as of 2026.
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)
VOO, the ETF Version
VOO is the Vanguard S&P 500 ETF. It tracks the exact same index as VFIAX and holds the same stocks.
How VOO Trades
VOO trades on an exchange just like a regular stock. You can buy or sell shares any time the market is open, and you see the price update in real time. You can use market orders, limit orders, and even fractional shares with many brokers.
Minimum Investment
There is no dollar minimum beyond the price of one share. If a broker offers fractional shares, you can start with as little as a few dollars. The expense ratio on VOO is 0.03 percent, even lower than VFIAX.
VFIAX vs VOO: The Real Differences
The holdings are essentially the same. The difference is in how you buy and hold them.
Trading Schedule
VOO can be traded all day. VFIAX prices once after the close. If you like to see live prices and place limit orders, the ETF can feel more flexible.
Cost to Get In
VFIAX has a 3,000 dollar opening minimum. VOO has none beyond the share price. For someone with a few hundred dollars to start, VOO is easier to access.
Where You Can Hold Them
VFIAX is generally only available inside Vanguard accounts or through some 401(k) plans. VOO trades on most US brokerages, including Fidelity, Schwab, and Robinhood. That makes the ETF a more flexible pick if you do not want a Vanguard account.
Reinvesting Dividends
Both funds pay dividends. VFIAX often makes automatic dividend reinvestment easier inside a Vanguard account. With VOO, you can set reinvestment through your broker, including Robinhood, but you may need to flip that setting on yourself.
Returns and Risk
Because both funds track the S&P 500, the returns line up year after year, with only tiny gaps from fees and how dividends are handled. The index has shown long periods of growth, but also sharp drops in 2008 and 2020.
A fund based on the S&P 500 is lower risk than holding one stock, since you own 500 companies at once. It is not a low-risk asset overall. The index can fall 20 percent or more in a bad year. Past performance does not guarantee future results.
Taxes and Account Type
ETFs like VOO are often slightly more tax efficient than mutual funds like VFIAX. Vanguard has a special structure that has narrowed that gap for its index mutual funds, but in a regular taxable account, many investors still slightly prefer the ETF for tax reasons.
In a Roth IRA, traditional IRA, or 401(k), the tax treatment depends on the account type. A tax professional can help you decide what fits your situation.
How to Buy Vanguard S&P 500 Funds
You have a few paths.
- Open an account directly with Vanguard if you want VFIAX or any other Admiral Shares mutual fund.
- Open a brokerage account elsewhere, such as Robinhood, Fidelity, or Schwab, and buy VOO from there.
- Inside a 401(k), check the plan menu for an S&P 500 index option, which is often a Vanguard fund.
Many brokers also offer recurring buys. You set a dollar amount and a schedule, and the broker buys the ETF for you. That helps with consistency over time.
Who These Funds Suit
Low-cost S&P 500 index funds tend to fit long-term investors who want broad US stock exposure with very low fees. They are often used as the core US stock piece of a wider portfolio that also holds bonds, international stocks, and cash.
They may not suit someone with a short time frame or someone who cannot tolerate large drops. Talk with a financial advisor before deciding how much to put into stock funds versus safer assets.
Frequently Asked Questions
Are VFIAX and VOO basically the same?
They track the same index and hold the same stocks. The structure is different. VFIAX is a mutual fund with a 3,000 dollar minimum and end-of-day pricing. VOO is an ETF with no opening minimum and live trading. Long-term returns are very similar.
Can I buy VFIAX on Robinhood?
No. Robinhood currently does not offer mutual funds like VFIAX. You can buy the ETF version, VOO, on Robinhood and most other US brokerages. To buy VFIAX you usually need a Vanguard account or a 401(k) that offers it.
Which has lower fees, VFIAX or VOO?
Both are very low. VOO has an expense ratio of about 0.03 percent as of 2026, while VFIAX is about 0.04 percent. On a 10,000 dollar position, that is a difference of around one dollar per year.
Is investing in a Vanguard S&P 500 fund safe?
It is lower risk than picking a single stock, but it is not safe in absolute terms. The S&P 500 can fall 20 percent or more during major market drops. Diversification across many stocks helps, but it does not remove market risk. Past performance does not guarantee future results.
