VOO vs FXAIX: ETF vs Fidelity's S&P 500 Index Fund

If your 401(k) or Fidelity brokerage account defaults to FXAIX while every investing forum seems to talk about VOO, it's a fair question: are these actually different, or is it the same S&P 500 exposure with a different label? Short answer — very close, but not identical. Here's what genuinely differs, what doesn't matter much, and how to think about which one fits your situation.

FXAIX's live price

FXAIX is a mutual fund, so unlike VOO it doesn't trade throughout the day — its price (net asset value, or NAV) is set once, after the market closes. Fetched live rather than typed in by hand:

What VOO and FXAIX each track

Both funds aim to track the S&P 500 index — roughly 500 large U.S. companies weighted by market capitalization. VOO is run by Vanguard; FXAIX is run by Fidelity, and launched in May 2011. Because they track the same index, their holdings are nearly identical at any given time — the same largest companies, in very similar proportions. Neither fund is trying to outperform the S&P 500; both are built to match it as closely as possible.

The real differences

• How and where you can buy it. VOO is an ETF, so it trades on an exchange and can be bought through essentially any brokerage. FXAIX is a Fidelity mutual fund — it's typically only available directly through a Fidelity brokerage or retirement account, which matters if you don't already have one.
• Pricing and trading. VOO's price moves throughout the trading day like a stock. FXAIX is priced once, after the market closes — you place an order during the day, but it fills at that day's closing NAV, not a price you watch move in real time.
• Expense ratio. Both funds are known for being among the cheapest ways to own the S&P 500, and the gap between them has historically been a fraction of a hundredth of a percent — genuinely small, but check current figures directly on Vanguard's and Fidelity's official pages before assuming either is cheaper.
• Minimum investment. Fidelity has removed minimums on many of its own index funds including FXAIX, and VOO's practical minimum depends on whether your broker supports fractional shares — check both directly, since policies change.

What doesn't matter as much as it seems

Because both funds track the same index, a long-term, buy-and-hold investor gets essentially the same underlying exposure either way — the same roughly 500 companies, moving together. Neither fund is designed to beat the other, so this isn't a bet on relative performance the way choosing between two individual stocks would be. For someone not actively trading intraday, the ETF-vs-mutual-fund structural difference matters far less than more basic decisions: how much you invest, how consistently, and for how long.

Which one should you actually hold

In practice, the decision is usually made for you by circumstance rather than performance. If your 401(k) plan only offers FXAIX, that answers the question — there's little reason to seek out VOO specifically when your available account already gives you essentially the same S&P 500 exposure through FXAIX. Conversely, if you're investing through a brokerage that doesn't offer Fidelity mutual funds, VOO (or a similar ETF) is the practical choice. If you genuinely have a free choice between the two in the same account, the decision mostly comes down to whether you have a preference for intraday trading (VOO) versus once-daily mutual fund pricing (FXAIX) — for a long-term holder, either is a reasonable, low-cost way to own the S&P 500.

Modeling either one

Because VOO and FXAIX track the same index, a growth projection for one works as a reasonable stand-in for the other, with the caveat that their expense ratios may differ slightly — a difference small enough to rarely change a long-term outcome meaningfully, but worth checking current figures rather than assuming. Use our S&P 500 calculator to project a plan for either fund, or see how VOO specifically compares to other alternatives in our VOO vs VTSAX article, which covers the same ETF-vs-mutual-fund structural question from Vanguard's side. This page is educational information, not a recommendation.