FXAIX is the ticker symbol for the Fidelity 500 Index Fund, a mutual fund that tracks the S&P 500 index. It holds the same roughly 500 large U.S. companies that make up the S&P 500, aiming to mirror that index’s performance as closely as possible. With an expense ratio of just 0.015%, it’s one of the cheapest index funds available anywhere, making it a popular core holding in retirement accounts and taxable portfolios alike.
How FXAIX Works
FXAIX is a passively managed fund, meaning there’s no portfolio manager picking stocks or making bets on which companies will outperform. Instead, the fund simply buys and holds the stocks in the S&P 500 in proportion to their weight in the index. When the index adds or removes a company, the fund follows suit. The result is a portfolio dominated by the largest U.S. companies by market value, spanning technology, healthcare, financials, consumer goods, and other sectors.
Because it’s a mutual fund rather than an ETF, FXAIX doesn’t trade on an exchange throughout the day. When you place a buy or sell order, it executes at the fund’s net asset value (NAV) calculated at the end of the trading day. This means you won’t get intraday pricing, but for long-term investors who aren’t trying to time the market hour by hour, that distinction rarely matters.
Costs and Minimum Investment
FXAIX charges a net expense ratio of 0.015% as of its most recent prospectus. On a $10,000 investment, that works out to $1.50 per year in fund fees. There is no sales charge (also called a load), so every dollar you invest goes directly into the fund. There is also no minimum investment requirement, which makes it accessible whether you’re starting with $50 or $50,000.
For context, this expense ratio is half the cost of Vanguard’s S&P 500 ETF (VOO), which charges 0.03%. The difference is small in dollar terms, but over decades of compounding, even fractions of a percent add up. On a $100,000 portfolio growing at 8% annually over 30 years, the gap between 0.015% and 0.03% in fees amounts to roughly $1,500 in extra costs for the more expensive option.
Dividends
FXAIX pays dividends from the underlying stocks in its portfolio. As of early 2026, the fund’s dividend yield sits around 1.22%. On a $10,000 investment, that translates to about $122 per year in dividend income. If you hold the fund in a retirement account like a 401(k) or IRA, you can reinvest those dividends automatically without triggering a tax event. In a taxable brokerage account, dividends are taxable in the year they’re paid.
FXAIX vs. S&P 500 ETFs
FXAIX, VOO (Vanguard’s S&P 500 ETF), and SPY (the original S&P 500 ETF from State Street) all track the same index, so their long-term returns are nearly identical. The differences come down to structure, cost, and how you trade them.
The biggest structural difference is that ETFs like VOO and SPY trade throughout the day at market prices, just like individual stocks. You can place limit orders, buy at 10 a.m., or sell at 2 p.m. FXAIX, as a mutual fund, only processes orders once per day at the closing NAV. If intraday trading flexibility matters to you, an ETF is the better fit. If you’re making regular contributions on a set schedule, the mutual fund structure works perfectly fine.
On taxes, ETFs have a slight structural advantage in taxable accounts. The way ETFs handle share creation and redemption means they typically generate fewer capital gains distributions than mutual funds. That said, FXAIX is passively managed with very low portfolio turnover, so it produces far fewer taxable events than an actively managed fund would. The tax efficiency gap between FXAIX and an S&P 500 ETF is narrower than you might expect.
If you already have a Fidelity account, FXAIX is especially convenient since you can buy it commission-free with no minimum. If your brokerage is Vanguard, VOO is the natural equivalent. The core investment is the same either way.
Where FXAIX Fits in a Portfolio
Most investors use FXAIX as a foundation. Because the S&P 500 represents roughly 80% of the total U.S. stock market by value, owning FXAIX gives you broad exposure to large-cap American companies in a single purchase. It covers household names in tech, healthcare, banking, retail, energy, and industrials without requiring you to research or buy individual stocks.
What it doesn’t cover is small-cap U.S. stocks, international markets, or bonds. A portfolio made up entirely of FXAIX would be 100% invested in large U.S. companies, which means you’d miss out on diversification across company sizes and geographies. Many investors pair FXAIX with a small-cap index fund, an international stock fund, and a bond fund to build a more complete portfolio.
FXAIX works in any account type: a workplace 401(k) (if your plan offers it), a traditional or Roth IRA, or a standard taxable brokerage account. Its zero-minimum requirement and rock-bottom fees make it one of the most straightforward ways to invest in the broad U.S. stock market.