VOO vs FXAIX: ETF vs Mutual Fund
Both track the S&P 500, and FXAIX is even slightly cheaper. The real decision is ETF versus mutual fund: intraday trading and tax efficiency versus automatic investing and fractional dollars.
Don't have time? Here's what you need to know:
- 1VOO and FXAIX track the identical S&P 500; FXAIX is marginally cheaper (~0.015% vs 0.03%), a negligible gap.
- 2The real difference is ETF vs mutual fund: VOO trades intraday and transfers between brokers; FXAIX prices once daily and is best kept at Fidelity.
- 3VOO is structurally more tax-efficient in a taxable account thanks to in-kind ETF redemptions; the edge vanishes in an IRA or 401(k).
- 4FXAIX shines for automatic whole-dollar investing at Fidelity; VOO wins for portability and taxable-account efficiency.
Same Index, Different Wrapper
VOO (Vanguard S&P 500 ETF) and FXAIX (Fidelity 500 Index Fund) both track the S&P 500 — the same roughly 500 large U.S. companies in the same weights — so their pre-fee returns are virtually identical. The interesting comparison isn't which index is better; it's that one is an ETF and the other is a traditional mutual fund. That structural difference shapes how you buy them, how they're taxed, and who each suits.
FXAIX is actually a touch cheaper on paper, at roughly 0.015% versus VOO's 0.03% — a difference of about $1.50 a year per $10,000, which is genuinely negligible. So fee isn't the deciding factor. The decision is really ETF mechanics versus mutual-fund mechanics.
How They Trade: Intraday vs End-of-Day
VOO is an ETF, so it trades on an exchange all day like a stock. You see a live price, you can place limit orders, and your trade executes immediately at the market price. FXAIX is a mutual fund, so it doesn't trade intraday at all: every buy or sell, no matter when you place it, executes once per day at the fund's net asset value calculated after the market closes.
For a long-term investor, end-of-day pricing is a non-issue and arguably a feature — it removes the temptation to day-trade your index fund. FXAIX also lets you invest exact dollar amounts (say, $500) automatically, including fractions of a share, which makes hands-off dollar-cost averaging seamless. VOO requires buying shares, though most brokers now offer fractional ETF shares too. If you want true set-and-forget automatic investing, the mutual-fund structure has historically been smoother.
Tax Efficiency: The ETF's Structural Edge
The most important practical difference is tax efficiency in a taxable account. ETFs like VOO use an "in-kind" creation and redemption mechanism that lets them flush out low-basis shares without triggering taxable capital-gains distributions to shareholders. As a result, broad-index ETFs rarely if ever pass through capital gains. A conventional mutual fund like FXAIX can be forced to sell holdings to meet redemptions, occasionally distributing capital gains that every shareholder owes tax on, even if they didn't sell.
In practice, FXAIX is an exceptionally well-run, low-turnover index fund and has historically kept capital-gains distributions very small — far smaller than an active fund. But the structural ceiling favors the ETF: in a taxable brokerage account, VOO has a modest, reliable tax-efficiency edge. Inside an IRA, 401(k), or other tax-advantaged account, this advantage disappears entirely, because distributions aren't taxed there in the first place.
| VOO | FXAIX | |
|---|---|---|
| Type | ETF | Mutual fund |
| Issuer | Vanguard | Fidelity |
| Index | S&P 500 | S&P 500 |
| Expense ratio | 0.03% | ~0.015% |
| Trading | Intraday on exchange | Once daily at NAV |
| Minimum | Price of 1 share (or fractional) | No minimum at Fidelity |
| Taxable-account efficiency | Higher (in-kind redemptions) | Slightly lower, but very good |
| Portability between brokers | Held anywhere | Best kept at Fidelity |
Important: FXAIX's tax edge only matters in a taxable brokerage account. Inside an IRA or 401(k), VOO and FXAIX are effectively identical on tax, so just pick the cheaper or more convenient one.
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Portability: Where You Hold It Matters
FXAIX is a Fidelity fund. You can hold it cleanly at Fidelity, but moving it to another broker can be awkward — some brokers won't hold another firm's proprietary mutual fund, and you may have to sell (a taxable event in a brokerage account) to transfer. VOO, as an ETF, trades and transfers freely at essentially every broker, so you're never locked in.
This makes the choice partly about where you invest. If Fidelity is your home base and likely to stay that way, FXAIX is a fantastic, ultra-cheap core holding. If you value the freedom to move your portfolio anywhere without selling, or you invest across multiple platforms, the ETF wrapper of VOO gives you portability that a proprietary mutual fund can't match.
Tip: If you live at Fidelity, FXAIX is a superb default. If you want a fund you can carry to any broker without a taxable sale, choose the ETF, VOO.
Which Should You Pick?
In a tax-advantaged account at Fidelity, FXAIX wins narrowly on its lower fee and effortless automatic investing in whole-dollar amounts. In a taxable account, VOO's structural tax efficiency and broker portability tip the scales, especially if you might ever change platforms. For most people the honest verdict is that both are excellent, nearly interchangeable ways to own the S&P 500, and the wrapper matters more than the fund.
If you want to compare the long-run impact of the tiny fee difference on your own contributions, the ETF return calculator makes it concrete — though spoiler, on the S&P 500 the difference between 0.015% and 0.03% is a rounding error compared with your savings rate.
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Frequently Asked Questions
Is VOO or FXAIX better?
They track the same S&P 500 and are nearly interchangeable. FXAIX (a Fidelity mutual fund) is slightly cheaper at ~0.015% and great for automatic whole-dollar investing at Fidelity. VOO (an ETF) trades intraday, is more tax-efficient in a taxable account, and transfers freely between brokers. Choose by account type and where you invest, not by the trivial fee gap.
Why is FXAIX cheaper than VOO but VOO is more tax-efficient?
Fidelity prices FXAIX at roughly 0.015% versus VOO's 0.03% to win cost-conscious investors, but the difference is about $1.50 a year per $10,000. VOO's tax efficiency comes from the ETF structure: in-kind redemptions let it avoid passing capital gains to shareholders, something a mutual fund like FXAIX can't do as cleanly. In a taxable account that structural edge can outweigh FXAIX's slightly lower fee.
Can I hold FXAIX at a broker other than Fidelity?
Often not cleanly. FXAIX is a proprietary Fidelity mutual fund, and many other brokers won't hold it or will charge to buy it. To move it elsewhere you may have to sell, which triggers capital-gains tax in a taxable account. VOO, as an ETF, transfers freely between virtually all brokers, which is a key advantage if you value portability.
Does FXAIX trade during the day like VOO?
No. FXAIX is a mutual fund, so all orders execute once per day at the closing net asset value, regardless of when you place them during the day. VOO is an ETF and trades intraday on an exchange at a live price. For long-term investors the end-of-day pricing of FXAIX is harmless and even discourages overtrading.
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Alex Harrington
CFA Level II Candidate, Finance & Economics
Alex Harrington is an independent ETF researcher and personal finance writer with over 8 years of experience analyzing exchange-traded funds. A CFA Level II candidate with a background in economics, Alex has reviewed 800+ ETFs and helped thousands of beginners build their first investment portfolios through clear, jargon-free education.
This content is for educational purposes only and does not constitute financial advice. Past performance does not guarantee future results. Consult a licensed financial advisor before making investment decisions.