FSKAX vs FXAIX: 7 Proven Differences That Matter in 2026

If you’ve searched FSKAX vs FXAIX and landed on three different comparison articles with three different sets of numbers, you’re not imagining things. One site says the expense ratio is 0.015%. Another rounds it to 0.02%. One says FSKAX holds “nearly 4,000” stocks, another says “more than 3,700,” and a third puts the exact figure at 3,753. Ten-year return numbers swing by almost a full percentage point depending on which snapshot date the page happened to be built from.

None of those sites are lying to you — index fund data just goes stale fast, and most comparison pages never get updated after they’re published. This guide pulls current numbers directly from Fidelity’s own fund lineup documentation and independent fund-data providers, explains exactly why FSKAX vs FXAIX comparisons disagree so often, and walks through which fund actually fits your situation in 2026.

Quick Facts: FSKAX vs FXAIX

What Is FSKAX vs FXAIX, Really?

FSKAX and FXAIX are both passively managed index mutual funds run by Fidelity, and both are famous for the same reason: rock-bottom cost. But they’re built to do different jobs.

FSKAX tracks the Dow Jones U.S. Total Stock Market Index, which means it holds roughly 3,700–3,800 U.S. companies spanning large-cap, mid-cap, small-cap, and micro-cap stocks. It’s designed to mirror the entire investable U.S. stock market in a single fund.

FXAIX tracks the S&P 500, the 500 largest publicly traded U.S. companies by market capitalization. It’s the same benchmark index that dominates financial news coverage and that most 401(k) plans use as their default “stock fund” option.

The FSKAX vs FXAIX decision ultimately comes down to one question: do you want to own the entire U.S. stock market, or just the largest 500 companies in it?

Background: How Each Fund Actually Works

Both funds launched within two months of each other in 2011, as part of Fidelity’s push to build a lineup of ultra-low-cost index funds that could go head-to-head with rival total-market and S&P 500 index funds from other major providers. Neither fund trades individual stocks based on manager judgment — both simply hold the securities in their target index, in roughly the same weightings, and rebalance periodically to stay aligned with that index.

Because they’re index funds rather than actively managed funds, turnover is low, tax efficiency is generally strong in taxable accounts, and the cost to you as an investor is close to negligible. That shared DNA is exactly why FSKAX vs FXAIX comparisons often conclude “either one works” — the real differences show up in what each fund actually contains, not in how it’s run.

If you’re building out a broader index-fund strategy beyond just picking one ticker, it’s worth browsing a wider range of investing guides before locking in your allocation, since fund selection is only one piece of the overall plan.

Core Deep-Dive: FSKAX vs FXAIX Head-to-Head

Expense Ratio

This is where the FSKAX vs FXAIX comparison gets confusing across the internet, because different sources round differently. Fidelity’s own fund lineup documentation lists both funds at a net expense ratio of 0.015% — among the cheapest index funds available anywhere, from any provider. Some third-party data aggregators round this up to 0.02% for display purposes, which is where the discrepancy across comparison sites comes from. Either way, on a $10,000 investment, the annual cost difference between the two funds is effectively zero — you’re paying $1.50 per year, per fund, per $10,000 invested.

Holdings and Diversification

This is the single biggest structural difference in the FSKAX vs FXAIX matchup. According to fund data compiled by AAII, FSKAX holds roughly 3,753 stocks, while FXAIX holds around 507. That’s roughly seven times more individual holdings in FSKAX, because it adds mid-cap, small-cap, and micro-cap companies on top of the same large-cap names FXAIX already owns.

In practice, that means FSKAX gives you a small built-in allocation to smaller companies that have historically added diversification benefits over full market cycles, while FXAIX concentrates your money entirely in already-established, large-cap businesses.

Performance

The performance side of the FSKAX vs FXAIX debate is where headlines get the most attention. Over the past decade, FXAIX has generally posted modestly higher returns than FSKAX, largely because large-cap U.S. stocks — and a handful of mega-cap technology names in particular — have outperformed the broader market for much of that stretch. That performance gap has narrowed and widened at different points depending on which years you measure, which is exactly why you’ll see different “FXAIX beat FSKAX by X%” figures depending on when a given article pulled its data. Neither fund has a permanent performance edge; the gap simply reflects how concentrated large-cap growth stocks have performed relative to the broader market in whatever window is being measured.

Risk and Correlation

Risk is another area where the FSKAX vs FXAIX comparison surprises people. Despite holding a different number of stocks, FSKAX and FXAIX move almost in lockstep — their historical price correlation sits close to 1.00, since FXAIX’s 500 holdings already make up roughly 85–90% of FSKAX’s total portfolio weight by value. Volatility and drawdown behavior between the two funds are nearly identical in most market conditions. This matters practically: owning both funds in the same account doesn’t meaningfully reduce your risk, because you’d mostly be duplicating the same large-cap exposure twice.

Tax Efficiency

Both funds are low-turnover index funds, which generally makes them tax-efficient choices for a taxable brokerage account. Neither fund has a structural tax advantage over the other in most standard scenarios — the bigger tax-planning question is usually which account type you’re using (a 401(k), a Roth IRA, or a taxable brokerage account), not which of these two index funds you pick within it.

FSKAX vs FXAIX in 2026

Heading into 2026, the FSKAX vs FXAIX conversation is shaped heavily by how top-heavy the S&P 500 itself has become. A small handful of mega-cap technology companies now represent an outsized share of the index’s total value, which means FXAIX’s performance is increasingly tied to the fortunes of those specific names. FSKAX dilutes that concentration slightly by spreading additional weight across thousands of smaller companies, even though its largest holdings still overlap heavily with FXAIX’s.

For investors weighing these funds inside a workplace retirement plan, it’s also worth understanding how index funds like these fit alongside other retirement vehicles you might be offered. If you’re comparing account types rather than just fund tickers, our breakdown of IUL vs 401(k) covers how a 401(k)’s investment options — including funds like FSKAX and FXAIX — stack up against insurance-based alternatives.

Breakdown: Which One Should You Actually Choose?

Choose FXAIX if: you specifically want exposure to the S&P 500 benchmark, you’re comparing your portfolio to “the market” as most financial media defines it, or your 401(k) plan only offers an S&P 500 index option.

Choose FSKAX if: you want the broadest possible U.S. equity exposure in a single fund, including small and mid-cap companies, and you’d rather not worry about whether you’re “missing out” on stocks outside the S&P 500.

Don’t bother owning both, at least not for diversification purposes. Because FXAIX’s holdings are almost entirely contained within FSKAX already, splitting money between the two mostly adds complexity without meaningfully changing your risk or return profile. Pick one as your core U.S. equity holding and build the rest of your portfolio around it.

FSKAX vs FXAIX: Side-by-Side Comparison

The table below condenses everything above into a single FSKAX vs FXAIX snapshot you can reference at a glance.

Practical Takeaways

Once you’ve weighed the FSKAX vs FXAIX trade-offs above, the decision isn’t one you need to overthink, but a few practical points are worth keeping in mind before you commit new contributions to either fund.

Whichever fund you choose, both are appropriate as a core, long-term holding rather than a short-term trade — index funds are built for buy-and-hold investing, not market timing. If you’re deciding how to actually get your money into the fund, whether as one upfront contribution or spread out over several months, our guide on dollar-cost averaging vs. lump sum investing walks through both approaches using a real $10,000 example, which applies just as directly to FSKAX or FXAIX as it does to any other index fund.

It’s also worth checking which of the two funds your specific 401(k) or brokerage platform actually offers before assuming you have a free choice — many workplace plans only list one of the two, which can settle the FSKAX vs FXAIX question for you by default. And if your goal is genuine diversification beyond U.S. large-cap and mid-cap stocks, neither fund alone gets you there; you’d still want to consider international equity or bond exposure separately.

People Also Ask

Is FSKAX or FXAIX better?

Neither fund is objectively “better” — FSKAX offers broader diversification across the entire U.S. market, while FXAIX offers concentrated exposure to the S&P 500’s largest companies. The better choice depends on whether you want total market coverage or large-cap-only exposure.

What is the difference between FSKAX and FXAIX?

FSKAX tracks the Dow Jones U.S. Total Stock Market Index and holds around 3,753 stocks across all market-cap sizes. FXAIX tracks the S&P 500 and holds around 507 large-cap stocks. Both carry the same 0.015% expense ratio.

Can you own both FSKAX and FXAIX?

You can, but it isn’t necessary for diversification. Because FXAIX’s holdings are already included within FSKAX, owning both mostly duplicates the same large-cap exposure rather than adding meaningfully different risk or return characteristics.

Does FSKAX include the same stocks as FXAIX?

Yes. FSKAX’s largest holdings overlap heavily with FXAIX’s entire portfolio, since both funds are weighted toward the same largest U.S. companies. FSKAX simply adds thousands of smaller companies on top of that overlap.

Which has more risk, FSKAX or FXAIX?

Historically, the two funds have shown very similar volatility and drawdown patterns, since their price correlation is close to 1.00. FSKAX’s small-cap exposure introduces a marginally different risk profile, but the practical difference in day-to-day risk is small.

What is the expense ratio of FXAIX and FSKAX?

Both funds carry a net expense ratio of 0.015%, according to Fidelity’s own fund documentation, making them two of the cheapest index funds available from any provider.

Should I switch from FXAIX to FSKAX?

Only if your goal is broader market exposure rather than S&P 500-specific exposure. Switching purely to chase recent performance is generally not a strong reason, since the performance gap between the two funds has historically been narrow and has shifted direction across different time periods.

Which fund has performed better historically?

Over most recent multi-year periods, FXAIX has posted slightly higher returns than FSKAX, largely due to the strong performance of large-cap growth stocks. This gap is not guaranteed to continue and has varied depending on the specific years measured.

Do FSKAX and FXAIX pay dividends?

Yes, both funds distribute dividends from the underlying stocks they hold, typically on a quarterly basis, along with periodic capital gains distributions.

What is the minimum investment for FSKAX and FXAIX?

Both funds have a $0 minimum investment requirement, making them accessible to investors starting with any contribution amount, including small recurring 401(k) or IRA contributions.

Is FSKAX riskier than FXAIX because of small-cap stocks?

FSKAX’s inclusion of small and mid-cap stocks adds a modest amount of additional volatility in theory, but in practice, because those stocks make up a small percentage of FSKAX’s total weighting, the real-world difference in risk between FSKAX and FXAIX has historically been minor.

Is it worth holding FSKAX and FXAIX together in a 401(k)?

Generally, no. Since FXAIX’s holdings are essentially a subset of FSKAX’s, holding both in the same 401(k) mostly means over-weighting large-cap stocks rather than achieving genuine diversification. Choosing one as your core U.S. equity fund and pairing it with other asset classes is typically more effective.