FZROX vs FSKAX: 12 Key Differences [2026 Update]

Choosing between two nearly identical total market index funds comes down to details most investors overlook. FZROX and FSKAX both offer broad US stock market exposure at rock-bottom costs, but differences in expense ratios, index methodology, and portability can meaningfully affect your long-term returns. Whether you're optimizing a taxable account or simplifying your portfolio, using top expense tracking tools alongside the right fund choice keeps your financial picture clear. Let's get started!

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FZROX vs FSKAX: 12 Key Differences [2026 Update]

Below you'll find detailed information about each option, including what makes them unique and their key benefits.

1. Expense Ratio

When comparing FZROX vs FSKAX, the expense ratio is often the deciding factor for cost-conscious investors. FZROX (Fidelity ZERO Total Market Index Fund) charges 0.00% — literally zero — while FSKAX (Fidelity Total Market Index Fund) charges 0.015% annually. On a $100,000 portfolio, that's roughly $15/year difference, which compounds meaningfully over decades.

Key comparison points:

• FZROX: 0.00% expense ratio (no annual fee)
• FSKAX: 0.015% expense ratio (~$15/year per $100K invested)
• Long-term impact favors FZROX slightly on cost alone

2. Index Tracked

The underlying index each fund tracks is a critical distinction in this comparison. FSKAX follows the Dow Jones U.S. Total Stock Market Index, a widely recognized benchmark, while FZROX tracks Fidelity's own proprietary Fidelity U.S. Total Investable Market Index. According to White Coat Investor, this means FZROX cannot be transferred in-kind to another brokerage — a meaningful portability disadvantage.

What this means practically:

• FSKAX tracks a standard, transferable index — usable at other brokerages
• FZROX uses a proprietary index — locked to Fidelity accounts only

3. Assets Under Management

Assets under management (AUM) signals investor confidence and fund liquidity in the FZROX vs FSKAX debate. FSKAX is the significantly larger fund, with over $80 billion in AUM, reflecting its longer track record since 2011. FZROX, launched in 2018, has grown rapidly but holds considerably less. Higher AUM in FSKAX generally means tighter bid-ask spreads and more established performance history for comparison.

Notable distinctions:

• FSKAX: ~$80B+ AUM, founded 2011 — longer data history
• FZROX: Smaller AUM, founded 2018 — newer but growing steadily

4. Number of Holdings

The difference in portfolio breadth is one of the clearest distinctions when comparing FZROX vs FSKAX. FZROX holds approximately 2,700+ stocks, while FSKAX holds over 3,800 securities, giving it broader exposure to small- and micro-cap companies. For investors who want maximum U.S. market coverage, that gap matters when evaluating total market diversification.

Key differences:

• FSKAX: ~3,800+ holdings covering nearly the entire U.S. market
• FZROX: ~2,700+ holdings, slightly less small-cap depth
• Both funds hold large-cap stocks as the majority of assets

5. Fund Inception and Longevity

FSKAX has a significantly longer track record than FZROX, which matters when assessing reliability and historical data depth. FSKAX launched in 2011, while FZROX debuted in August 2018 as part of Fidelity's zero-fee fund lineup. Investors comparing these two funds should note that FSKAX offers over a decade of performance history, providing more data points through multiple market cycles including the 2018 correction and 2020 crash.

Longevity snapshot:

• FSKAX inception: September 8, 2011
• FZROX inception: August 2, 2018
• FSKAX has ~7 additional years of verifiable performance data

6. Historical Performance

When sizing up FZROX against FSKAX on returns, the two funds track nearly identically over comparable periods — which is expected given their similar compositions. According to PortfoliosLab, annualized return differences are typically under 0.1%, making performance a near tie. The slight variance stems from index methodology and small-cap weighting differences rather than any meaningful manager advantage.

Performance notes:

• 10-year annualized returns are virtually identical between the two
• Short-term gaps rarely exceed 0.05–0.10% annually

7. Recent Returns

When comparing FZROX vs FSKAX, recent performance data shows the two funds tracking extremely closely. FZROX has occasionally edged ahead due to its zero expense ratio, meaning every basis point stays in your pocket rather than covering fund costs. The difference is typically measured in fractions of a percent annually.

Key figures:

• Both funds closely mirror total US market performance
• FZROX's 0% expense ratio vs FSKAX's 0.015% gives a slight return edge
• Short-term return gaps between the two are rarely meaningful

8. 1-Year and 3-Year Returns

Over longer horizons, the FZROX and FSKAX comparison remains remarkably tight, as both track broad US market indexes with nearly identical holdings. According to PortfoliosLab, annualized return differences over 1- and 3-year periods typically fall within 0.01–0.05%, well within normal tracking variance. Neither fund consistently outperforms the other over multi-year windows.

• 3-year annualized returns are statistically near-identical for both funds
• FZROX's zero expense ratio theoretically compounds the slight edge over time

9. Volatility

Volatility is essentially a non-factor when deciding between these two funds, since both hold the full US stock market and respond identically to market swings. Standard deviation and beta figures for FZROX and FSKAX are virtually indistinguishable because their underlying indexes overlap by over 99% in market-cap weighting. Neither fund offers a meaningful volatility advantage over the other.

• Both carry similar risk profiles — no defensive edge on either side
• Volatility is driven by total market conditions, not fund selection here

10. Dividend Yield

Dividend yield is a practical comparison point between FZROX and FSKAX because both funds distribute income, but at slightly different rates. FSKAX has historically offered a marginally higher dividend yield due to its broader inclusion of small-cap dividend-paying stocks. For income-focused investors, this difference—while small—can influence which fund better fits a dividend reinvestment strategy.

Key differences:

• FSKAX yield: approximately 1.3–1.5% annually
• FZROX yield: slightly lower, typically 1.2–1.4% annually
• Both pay quarterly distributions suitable for DRIP strategies

11. Tax Efficiency and Strategy

When deciding between these two Fidelity index funds, tax efficiency matters—especially in taxable brokerage accounts. FZROX has a structural advantage here: its zero-expense-ratio design and lack of licensing fees reduce the need for frequent portfolio rebalancing, which minimizes taxable capital gains distributions. FSKAX, while also tax-efficient, has occasionally distributed small capital gains. According to White Coat Investor, both funds suit tax-advantaged accounts like IRAs equally well.

• FZROX: no recorded capital gains distributions historically
• FSKAX: rare but occasional small capital gains events

12. Overall Recommendation

For most long-term investors choosing between FZROX and FSKAX, FZROX is the stronger pick for cost-conscious buy-and-hold investors who stay within the Fidelity ecosystem—its 0% expense ratio provides a guaranteed cost edge. FSKAX makes more sense if you plan to transfer assets between brokerages, since FZROX cannot be transferred in-kind and would require liquidation. As noted by Physician on FIRE, the performance gap between the two is minimal over time.

• Choose FZROX: staying at Fidelity, maximizing cost savings
• Choose FSKAX: flexibility to move brokers without forced liquidation

Final Words

Your best bet between FZROX and FSKAX depends on whether you prioritize Fidelity's zero-expense ratio or broader index flexibility across all 12 options explored here — pair your decision with free budget templates to keep your investment strategy on track.