The S&P 500 index has returned an average of about 10% per year over the long run. That track record has made S&P 500 funds one of the most popular investments on earth. But when you go to buy one, you face a choice: index mutual fund or ETF?
They both track the same 500 companies. They both offer broad diversification at low cost. But the mechanics are different in ways that can matter depending on how you invest.
What Is an S&P 500 Fund?
An S&P 500 fund holds shares of all 500 companies in the S&P 500 index, proportionally weighted by market cap. Instead of picking individual stocks, you own a tiny slice of Apple, Microsoft, Amazon, and hundreds of other companies in a single purchase.
The goal is to match the performance of the index, not beat it. Because they are passively managed, these funds have very low fees compared to actively managed funds.
Both mutual funds and ETFs can track the S&P 500. The difference is in how they are structured, traded, and taxed.
How S&P 500 Mutual Funds Work
Mutual funds pool money from many investors and invest it as a single portfolio. You buy and sell shares at the fund's net asset value (NAV), which is calculated once per day after the market closes.
This means you cannot trade an index mutual fund in real time. Whatever price the NAV settles at that day is the price you get, whether you placed your order at 9 a.m. or 3 p.m.
Mutual funds often have minimum investment requirements. Vanguard's VFIAX, for example, requires a $3,000 minimum to open. Fidelity's FZROX has no minimum, which makes it more accessible for beginners.
Expense ratios on top S&P 500 mutual funds are very competitive. Fidelity FXAIX charges 0.015% per year. That is $1.50 on a $10,000 investment. If you want to see how FXAIX and other leading funds stack up against each other, our guide to the best S&P 500 mutual funds covers the full comparison.
How S&P 500 ETFs Work
An ETF (exchange-traded fund) is a fund that trades on a stock exchange just like a share of stock. You buy and sell it at any point during market hours, and the price fluctuates throughout the day based on supply and demand.
ETFs typically have no minimum investment beyond the price of one share. Vanguard's VOO, one of the most popular S&P 500 ETFs, trades at roughly $500 per share as of 2026. Some brokers offer fractional shares, lowering the entry point further.
Expense ratios on ETFs are also very low. VOO charges 0.03% per year. SPY, the oldest S&P 500 ETF, charges 0.0945%.
Key Differences: Mutual Funds vs ETFs
Cost
Both are cheap, but ETFs have a slight edge at many fund families. VFIAX (mutual fund) charges 0.04% vs VOO (ETF) at 0.03%. The gap is small but compounds over decades.
Tax Efficiency
ETFs are generally more tax-efficient than mutual funds, especially in taxable accounts. Mutual funds sometimes distribute capital gains to all shareholders, even if you did not sell. ETFs are structured to minimize those distributions. In a tax-advantaged account like an IRA or 401(k), this difference disappears.
Trading
Mutual funds price once per day at NAV. ETFs trade in real time during market hours like a stock. For long-term investors, this difference rarely matters. For those who want to act on market conditions, ETFs offer more flexibility.
Investment Minimums
Many mutual funds require $1,000 to $3,000 to open an account. ETFs can be purchased for the price of one share, or less if fractional shares are available.
VFIAX vs VOO: A Side-by-Side Example
Both VFIAX and VOO are Vanguard S&P 500 funds. They hold nearly identical portfolios. For a deeper dive into how they differ, see our dedicated VFIAX vs VOO comparison.
| Feature | VFIAX (Mutual Fund) | VOO (ETF) |
|---|---|---|
| Expense ratio | 0.04% | 0.03% |
| Minimum investment | $3,000 | ~$500 (1 share) |
| Trading | End of day NAV | Intraday |
| Tax efficiency | Good | Slightly better |
| Dividends | Reinvested automatically | Manual or DRIP |
For most long-term investors, both are excellent choices. The ETF version gives you slightly lower cost and better tax efficiency in a taxable account. The mutual fund version can be easier to automate with round-dollar contributions.
Which One Is Right for You?
If you are investing inside a 401(k) or individual retirement account, the tax efficiency advantage of ETFs disappears. The mutual fund's automatic reinvestment features may make it slightly simpler to manage. Either way, costs are low enough that the difference in outcome over time is minimal.
If you are investing in a taxable brokerage account, the ETF's tax efficiency gives it a real edge. You avoid unexpected capital gains distributions and keep more of your returns.
If you want to get started with an S&P 500 fund, one platform to consider is Robinhood. Robinhood offers commission-free trading on ETFs like VOO, and you can buy fractional shares starting at $1. That means you do not need to wait until you have $500 for a full ETF share or $3,000 for a mutual fund minimum.
Investing in any fund involves risk. You could lose money, including your principal. Consider your investment goals and time horizon before investing.
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Common Scenarios
Starting with a small amount: If you have $100 to invest, an ETF with fractional share support is your best option. Mutual fund minimums of $1,000 or $3,000 would lock you out.
Automating regular contributions: Mutual funds often make it easier to auto-invest a fixed dollar amount each month. ETFs require you to buy whole shares (or use a platform that supports fractional share recurring buys).
Investing in a taxable account: ETFs win on tax efficiency. Capital gains distributions from mutual funds can create an unexpected tax bill.
Inside an IRA or 401(k): Either works well. Focus on the expense ratio. The lower the better.
Frequently Asked Questions
Are S&P 500 mutual funds and ETFs the same investment?
They track the same index and hold virtually the same stocks, but they are different fund structures. Mutual funds price once a day at NAV. ETFs trade on an exchange like a stock throughout the day. For long-term buy-and-hold investors, performance is nearly identical after accounting for fees.
Which has lower fees, S&P 500 mutual funds or ETFs?
Both are very cheap. Some of the lowest-cost S&P 500 mutual funds charge 0.015% to 0.04% per year. Top ETFs charge 0.03%. The difference is small, but ETFs have a slight edge at most fund families.
Can I buy an S&P 500 ETF inside a Roth IRA?
Yes. You can hold ETFs inside any IRA. In fact, ETFs are a common choice for IRA investors because of their low costs and flexibility. The tax efficiency advantage of ETFs is less relevant inside a Roth IRA since all qualified withdrawals are already tax-free.
What is the minimum to buy an S&P 500 ETF?
The minimum is typically the price of one share. For VOO, that is roughly $500. For SPY, around $550. Some brokers offer fractional shares, letting you start with as little as $1. Mutual fund minimums are usually $1,000 to $3,000, though some funds like Fidelity's FXAIX have no minimum. If you are ready to take the first step, our guide on how to invest in the S&P 500 walks through the full process. When choosing between the two most widely owned S&P 500 ETFs, a SPY vs VOO comparison breaks down cost, liquidity, and which suits long-term holders better.
