FXAIX vs SPY: Which Is the Better Pick in 2026?

Overview

FXAIX and SPY both track the S&P 500 Index, holding the same underlying 500 large-cap U.S. stocks in nearly identical weightings. The key difference is structure: FXAIX is a mutual fund sold through Fidelity's platform, while SPY is an ETF traded on exchanges like a stock. That structural difference drives divergences in cost, tax efficiency, and how you buy and sell them.

How they differ

SPY's expense ratio of 0.10% beats FXAIX's 0.49% by a wide margin—that's 39 basis points of annual drag that compounds over decades. Both track the S&P 500 with a beta of 1.0 and distribute quarterly at nearly identical yields (SPY 0.98%, FXAIX 1.03%), so performance before expenses should be nearly identical. The structural difference matters most at tax time: ETFs like SPY can be more tax-efficient because of their in-kind creation and redemption mechanism; mutual funds like FXAIX may distribute capital gains from portfolio turnover, though Fidelity's index fund design minimizes that. FXAIX has a longer track record (inception February 1988 vs. January 1993), though both have decades of history. AUM is comparable ($833B vs. $812B), meaning both are massive and highly liquid.

Who each is best for

FXAIX: Fits investors who already have a Fidelity brokerage or retirement account and prefer the simplicity of a mutual fund with automatic dividend reinvestment and no trading spreads. Also suits buy-and-hold investors indifferent to paying a bit more in expenses for convenience within a single platform ecosystem.

SPY: Designed for investors who can access a brokerage account and want the lowest possible cost—the 39-basis-point expense advantage compounds significantly over 20+ years. Also fits traders or tactical allocators who need intraday liquidity and the ability to buy or sell at market prices during the trading day.

Key risks to know

• Expense-ratio drag. SPY's lower cost translates to higher net returns over time; an investor in FXAIX will see 39 basis points per year flow to Fidelity instead of staying invested. Over 30 years, that gap alone can meaningfully reduce wealth.

• Trading spread vs. no friction. SPY trades on an exchange with a bid-ask spread (typically a few cents per share); FXAIX trades at its daily NAV with no spread. For small positions or frequent traders, SPY's spread erodes returns; for large positions held long-term, the spread is negligible.

• Tax-loss harvesting mechanics. SPY's ETF structure may allow for more efficient tax-loss harvesting in taxable accounts, particularly because it's easy to swap into a nearly identical fund or back without account friction. FXAIX's mutual fund structure doesn't prevent loss harvesting but requires more care around the 30-day wash-sale window.

• S&P 500 concentration risk. Both funds hold the same 500 stocks with identical weightings; neither diversifies beyond large-cap U.S. equities. Performance is fully dependent on the S&P 500's health.

Bottom line

If you're optimizing for the lowest cost and can trade on an exchange, SPY's 39-basis-point expense advantage and ETF tax efficiency give it a structural edge over decades. If you're already a Fidelity customer comfortable with mutual fund mechanics and value the convenience of no trading spreads, FXAIX's simplicity and longer track record justify the slightly higher fee. Both track the same index and will move in lockstep—the choice hinges on platform, access, and how much you value expense efficiency against convenience. Past performance is no guarantee of future results.