Choosing between two nearly identical index funds shouldn't be complicated — yet FZROX and FSKAX trip up even experienced investors. FZROX charges a true 0.00% expense ratio while FSKAX comes in at 0.015%, a difference that adds up to $1.50 per year per $10,000 invested. Both funds offer broad U.S. market exposure, but they differ in index tracked, holdings count, and where you can hold them — details that matter more than most investors realize. For broader investment platform comparisons or free financial education resources to sharpen your strategy, we've got you covered. Here's exactly how these two Fidelity funds stack up.
Quick Answer
FZROX has a 0.00% expense ratio versus FSKAX at 0.015%, saving $1.50 annually per $10,000 invested. Both provide broad U.S. market exposure but track different indexes and hold different numbers of stocks. FZROX is only available at Fidelity, while FSKAX can be held at other brokerages — a key distinction depending on your platform.
Jump to
Summary Table
| Item Name | Price Range | Best For | Website |
|---|---|---|---|
| Expense Ratio | FZROX: 0.00% / FSKAX: 0.015% | Cost-minimizing investors | Visit Site |
| Fund Size and Holdings | FSKAX: ~$125B / FZROX: ~$33.7B | Investors prioritizing scale and liquidity | Visit Site |
| Index Tracked | No direct fee difference | Investors who care about index methodology | Visit Site |
| Diversification | FSKAX: ~3,900 stocks / FZROX: ~2,700 stocks | Investors wanting maximum stock coverage | Visit Site |
| Fund Availability | FZROX: Fidelity only / FSKAX: Transferable | Investors planning to switch brokerages | See details |
| Historical Performance | Returns within ~0.01% of each other | Long-term buy-and-hold investors | See details |
| Year-to-Date Returns | Virtually identical annually | Investors tracking short-term benchmarks | See details |
| Fund Existence | FSKAX: Since 2011 / FZROX: Since 2018 | Investors valuing longer track records | See details |
| Best Choice for Cost-Conscious Investors | FZROX: 0.00% expense ratio | Fidelity account holders focused on fees | Visit Site |
FZROX vs FSKAX: 9 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
The expense ratio is one of the most critical differentiators when comparing FZROX vs FSKAX. FZROX (Fidelity ZERO Total Market Index Fund) charges 0.00% — literally zero — while FSKAX (Fidelity Total Market Index Fund) charges 0.015% annually. Over decades of compounding, even this razor-thin difference can meaningfully impact long-term returns, making cost comparison essential for cost-conscious investors choosing between these two funds.
Key cost facts:
- FZROX: 0.00% expense ratio (no annual fee)
- FSKAX: 0.015% expense ratio (~$1.50 per $10,000 invested annually)
2. Fund Size and Holdings
When evaluating these two Fidelity total market funds, fund size and number of holdings reveal meaningful structural differences. FSKAX holds approximately 3,800+ individual stocks, closely mirroring the broad U.S. market, while FZROX holds around 2,700+ stocks using a proprietary index. According to PortfoliosLab, both funds maintain billions in assets under management, offering strong liquidity and stability for long-term investors.
Holdings comparison:
- FSKAX: ~3,800+ holdings, broader small-cap exposure
- FZROX: ~2,700+ holdings, slightly less small-cap depth
3. Index Tracked
The index each fund tracks is arguably the sharpest structural distinction in the FZROX vs FSKAX debate. FSKAX follows the Dow Jones U.S. Total Stock Market Index, a well-established third-party benchmark. FZROX tracks Fidelity's own proprietary zero-fee index, which is why it can eliminate expense ratios entirely. This means FZROX cannot be directly replicated at another brokerage, creating a potential portability concern if you ever transfer your account.
Index details:
- FSKAX: Dow Jones U.S. Total Stock Market Index (transferable)
- FZROX: Fidelity U.S. Total Investable Market Index (Fidelity-exclusive)
4. Diversification
Both FZROX and FSKAX offer broad U.S. market exposure, but their diversification profiles differ in index construction. FZROX tracks the Fidelity U.S. Total Investable Market Index, while FSKAX follows the Dow Jones U.S. Total Stock Market Index — resulting in slightly different stock counts and weighting methodologies. Investors comparing these two funds should examine how each index samples small-cap and mid-cap holdings, since those tiers drive meaningful long-term return differences.
Key distinctions:
- FZROX holds ~2,700 stocks; FSKAX holds ~3,800+ stocks
- Broader holding count in FSKAX means marginally deeper small-cap exposure
5. Fund Availability
One practical difference between these two total market funds is where you can actually hold them. FZROX is exclusive to Fidelity accounts — it cannot be transferred in-kind to another brokerage. FSKAX, while also a Fidelity fund, is a traditional mutual fund that offers slightly more flexibility for investors who may eventually consolidate accounts elsewhere. For investors firmly committed to Fidelity, this distinction is largely irrelevant.
Availability breakdown:
- FZROX: Fidelity only, no transfer-in-kind to outside brokerages
- FSKAX: Fidelity-based but treated as a standard mutual fund structure
6. Historical Performance
When choosing between these two index funds, historical returns offer useful context — though both track the total U.S. stock market and perform nearly identically over time. According to PortfoliosLab, annualized return differences between FZROX and FSKAX are typically under 0.10%, making past performance a weak differentiator. The zero expense ratio of FZROX gives it a slight theoretical edge in net returns over long holding periods.
- 10-year annualized returns are nearly identical between both funds
- FZROX's 0% expense ratio vs. FSKAX's 0.015% compounds slightly over decades
7. Year-to-Date Returns
When comparing FZROX vs FSKAX, year-to-date returns reveal how closely these two funds track each other in practice. Because both follow broad U.S. total market indexes, their YTD performance figures typically differ by only a fraction of a percent in any given year, confirming they behave as near-identical investments for most time horizons.
Key performance facts:
- Historical annual return gap between the two funds is often under 0.05%
- Short-term divergence is usually driven by index methodology, not fund management
8. Fund Existence
FSKAX has been available since 2011, while FZROX launched in 2018 as part of Fidelity's zero-fee fund lineup. This difference in track record matters when evaluating FZROX vs FSKAX because FSKAX carries a longer auditable performance history, giving data-driven investors more backtested evidence. FZROX's shorter history means less data during major market cycles like 2011–2013.
Tenure snapshot:
- FSKAX: 13+ years of performance data
- FZROX: launched August 2018, roughly 6 years of history
9. Best Choice for Cost-Conscious Investors
For investors prioritizing the absolute lowest fees, FZROX wins the cost comparison decisively — its 0.00% expense ratio versus FSKAX's 0.015% means zero annual drag on returns. While 0.015% is already extremely low, FZROX literally costs nothing to hold, making it the logical pick for fee-sensitive Fidelity account holders who plan to stay within the Fidelity ecosystem long-term. According to Physician on FIRE, the practical dollar difference is negligible but real over decades.
- FZROX expense ratio: 0.00% — no annual fee whatsoever
- FSKAX expense ratio: 0.015% — roughly $1.50 per $10,000 invested annually
Final Words
Your best bet depends on whether you prioritize slightly lower fees with FZROX or broader availability with FSKAX — both are excellent total market index funds. Pair your choice with top expense tracking apps to keep your portfolio costs in check.