FXAIX vs FZROX: Which Fidelity Zero-Fee Fund Is Better? (2026)
FXAIX and FZROX are two of the most compelling mutual funds available — not because of what they charge (both are free), but because of what they represent: the choice between America's 500 largest companies and the entire U.S. stock market. Here's how they actually compare.
FXAIX vs FZROX: At a Glance
| Metric | FXAIX | FZROX |
|---|---|---|
| Fund Name | Fidelity 500 Index Fund | Fidelity ZERO Total Market Index Fund |
| What It Tracks | S&P 500 (500 stocks) | Fidelity U.S. Total Investable Market (3,000+ stocks) |
| Expense Ratio | 0% (both) | |
| Minimum Investment | $0 (both) | |
| Total Assets | $715B | $32B |
| 1-Year Return | 16.22% | 16.79% |
| 3-Year Annualized | 19.13% | 19.07% |
| 5-Year Annualized | 11.64% | 10.77% |
| Volatility (Std Dev) | 13.24% | 13.59% |
| Distribution Yield | 1.16% | 1.07% |
| Inception Date | May 2011 | August 2018 |
| Morningstar Rating | ★★★★ (4) | ★★★ (3) |
| Proprietary Index? | No (S&P 500) | Yes (Fidelity only) |
*Returns as of April 2026. Past performance does not guarantee future results.
The Core Difference: 500 Stocks vs. 3,000+ Stocks
FXAIX tracks the S&P 500 — the 500 largest U.S. companies by market capitalization. This covers roughly 80% of the total U.S. stock market value.
FZROX tracks the Fidelity U.S. Total Investable Market Index — which includes large-cap, mid-cap, and small-cap stocks. It holds 3,000+ companies and covers essentially the entire investable U.S. equity market.
In practical terms, FXAIX is a subset of FZROX. Every stock in FXAIX is also in FZROX — but FZROX adds thousands of mid-size and small companies that don't make the S&P 500 cutoff.
Performance: It's Close, But Not Identical
Over the past year, FZROX has slightly outperformed FXAIX (16.79% vs 16.22%). Over three years, they're virtually tied. The five-year picture shows FXAIX ahead (11.64% vs 10.77%) — likely because the last five years were dominated by large-cap tech stocks (NVIDIA, Apple, Microsoft) that make up a larger slice of FXAIX.
When large caps lead, FXAIX wins. When mid and small caps run, FZROX gains ground. Neither consistently outperforms — it depends on the market cycle.
Diversification Edge: FZROX
FZROX's structural advantage is clear: by holding 3,000+ stocks instead of 500, you get:
- Exposure to mid-cap growth companies before they're large enough for the S&P 500
- Small-cap representation that captures the historical long-term outperformance of smaller companies
- Less concentration risk — the top 10 holdings in FXAIX represent ~35% of assets; FZROX's top 10 are a smaller percentage
Academic research consistently shows that total market indexes edge out S&P 500 indexes over very long periods (20+ years), driven by the small-cap premium. That gap may or may not materialize in your investment horizon.
The Problem with FZROX: Proprietary Index
FXAIX tracks the S&P 500 — a widely recognized, independently maintained index. If you ever leave Fidelity, you can replicate FXAIX's performance with VFIAX (Vanguard), SWPPX (Schwab), VOO, or IVV.
FZROX tracks a Fidelity proprietary index. There's no exact equivalent at other brokerages. If you move to Vanguard, the closest match is VTSAX — but it charges 0.04%, has a $3,000 minimum, and tracks a slightly different index. For a long-term Fidelity investor, this is a minor concern. For anyone who might switch brokerages, it's worth noting.
FXAIX vs FZROX: Which Should You Pick?
Choose FXAIX if you…
- ✅ Want the simplicity of a pure S&P 500 fund
- ✅ Value portability — you might leave Fidelity someday
- ✅ Prefer slightly lower volatility (large-cap only)
- ✅ Have a shorter time horizon where large-cap stability matters
Choose FZROX if you…
- ✅ Want maximum U.S. market diversification
- ✅ Plan to stay at Fidelity long-term
- ✅ Have a 20+ year horizon (small-cap premium can compound)
- ✅ Want mid and small-cap exposure without buying separate funds
Our take: For most Fidelity investors committed to staying at Fidelity, FZROX is the better single-fund choice. Broader diversification at zero cost is a hard combination to beat. If portability matters to you — or you might consolidate accounts at Vanguard later — stick with FXAIX.
Frequently Asked Questions
What is the difference between FXAIX and FZROX?
FXAIX tracks the S&P 500 (500 large-cap stocks, $715B AUM) while FZROX covers the entire U.S. market (3,000+ stocks, $32B AUM). Both charge 0% with no minimums. FZROX offers broader diversification; FXAIX tracks a portable, widely-recognized index.
Is FZROX better than FXAIX?
For most long-term Fidelity investors, yes — FZROX's broader market coverage gives you better diversification at the same cost (0%). The main exception: if you might switch brokerages, FXAIX's S&P 500 tracking is easier to replicate elsewhere.
Can I hold both FXAIX and FZROX?
Yes, but it creates heavy overlap — every FXAIX holding is already in FZROX. Holding both just overweights large-cap stocks. If you want genuine diversification, pick one. FZROX alone gives you everything FXAIX does, plus mid and small caps.
Why does FZROX have so much less AUM than FXAIX?
FXAIX has been around since 2011 and has had more time to accumulate assets. FZROX launched in 2018. Both are sizable funds — $715B vs $32B — but FXAIX's longer track record and name recognition have driven more inflows.
What is the FZROX equivalent at Vanguard?
The closest match is VTSAX (Vanguard Total Stock Market Index Fund). It charges 0.04% and requires a $3,000 minimum — more expensive and less accessible than FZROX's 0%/$0. If you're at Fidelity, FZROX is the better deal.
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