FSKAX vs FZROX: Which Should You Pick?
FZROX charges nothing and FSKAX 0.015%, $1.50 a year per $10,000. FZROX is generally held only at Fidelity. Which to use in an IRA, which in taxable, and why.
FSKAX and FZROX are Fidelity’s two total U.S. stock market index funds. FSKAX charges 0.015% and tracks the Dow Jones U.S. Total Stock Market Index. FZROX charges nothing and tracks Fidelity’s own U.S. Total Investable Market Index. The fee gap is $1.50 a year on $10,000. The difference that matters more is where you can hold FZROX: its prospectus limits it to Fidelity brokerage accounts.
Quick answer
In a Fidelity IRA, buy FZROX: it costs nothing, and if you ever move the account you can sell inside the IRA without tax. In a taxable account you might move someday, FSKAX or a total-market ETF such as VTI keeps your options open, because FZROX can generally be held only at Fidelity and leaving would mean selling it and paying tax on the gains. Whichever you already own, keep it; $1.50 per $10,000 a year does not justify a taxable sale.
| FSKAX | FZROX | |
|---|---|---|
| Expense ratio | 0.015% | 0.00% |
| Index | Dow Jones U.S. Total Stock Market | Fidelity U.S. Total Investable Market (proprietary) |
| Holdings | 3,755 | 2,636 |
| Fund assets | $141.6 billion | $41.2 billion |
| Where you can hold it | Fidelity, retirement accounts, or through an adviser | Fidelity brokerage accounts only |
| Annual return, Sept 2018 to Sept 2026 | 13.71% | 13.85% |
| Last capital gains payout | April 2019 | December 2021 |
| Dividends paid | April and December | December |
Fidelity summary prospectuses (FSKAX April 29, 2026; FZROX December 30, 2025) and fund research pages; holdings at August 31, 2026, assets at September 30, 2026. Returns are Summitward calculations from daily total-return prices, August 31, 2018 to September 30, 2026.
FZROX has done slightly better
From August 2018, when FZROX launched, to September 2026, FZROX returned 13.85% a year and FSKAX 13.71%. FZROX was ahead in every rolling three-year and five-year window in that period, by a median of 0.17 points a year. That is more than the 0.015-point fee gap, so the indexes and how each fund tracks them account for most of it. Securities lending is too small to explain it: FZROX earned $1.8 million from lending in its fiscal year to October 2025, about 0.006% of its assets at that year-end. Eight years is a short window, and a different stretch could favor the Dow Jones index; the funds’ monthly returns were 0.9999 correlated.
The constraint is portability
FZROX’s prospectus says shares are available only to individual retail investors buying through a Fidelity brokerage account, plus certain broker-dealers with Fidelity arrangements. If you leave Fidelity, you can keep the account open and leave FZROX in it, or sell. In an IRA, selling costs no tax. In a taxable account, selling realizes every dollar of gain at once. FSKAX’s prospectus lists more channels, including investment professionals, but before moving it check whether the new broker will hold it and what it charges to buy more. Whole shares of a total-market ETF move in kind to any broker; fractional shares are often sold in the transfer.
Our guide to the ZERO funds covers this trade-off in more detail, and FZROX vs VTI compares FZROX with the ETF route.
Switching an existing position
On a $100,000 holding, moving from FSKAX to FZROX saves $15 a year. In a taxable account, $40,000 of gains taxed at 15% is $6,000, which is 400 years of that saving. The calculator below starts with FSKAX as the current fund and FZROX as the replacement; enter your own position.
Who should pick which
Pick FSKAX if you
- Invest in a taxable account and might leave Fidelity.
- Want an index run by an outside provider.
- Already own it with gains; keep it.
Pick FZROX if you
- Invest in a Fidelity IRA or Roth IRA.
- Plan to stay at Fidelity for the long run.
- Already own it with gains; keep it.
Sources and related reading
- Fidelity Total Market Index Fund (FSKAX) summary prospectus (April 29, 2026) and fund research page.
- Fidelity ZERO Total Market Index Fund (FZROX) fund research page, summary prospectus (December 30, 2025) and annual report for the year ended October 31, 2025, on SEC EDGAR.
- FZROX vs VTSAX, VTSAX vs FSKAX, VTI vs SCHB, and when switching to a cheaper index fund pays.
Want to see how this fits your whole portfolio?
Summitward turns portfolio, tax, and life-planning tradeoffs into decisions you can act on, including overlap, concentration, and tax-location analysis across your accounts.