Wealthy PotFSKAX vs VOO: 88% Overlap, So You Are Really Choosing Total Market or the S&P 500
FSKAX and VOO are both cheap, both index funds, and they share most of their money. What separates them is coverage and wrapper. FSKAX is Fidelity's total US market mutual fund, tracking an index of about 5,000 stocks for 0.015% a year. VOO is Vanguard's S&P 500 ETF, holding the 500 large companies in that index for 0.03%. Matching their SEC holdings filings, the overlap was 87.8%, and 99.6% of VOO's money sat in stocks FSKAX also held. The rest of FSKAX, about 11%, is mid and small companies. Over the ten years to 30 September 2026 that slice cost FSKAX: VOO returned 15.29% a year at NAV and FSKAX 14.69%.
Table of Contents
The Short Answer
- Fees: 0.015% vs 0.03%. $1.50 against $3 a year on $10,000. The prospectus cost examples over ten years: $19 and $39.
- Overlap: 87.8%. 99.6% of VOO was in stocks FSKAX held; 88.9% of FSKAX was in VOO stocks. Our calculation from FSKAX's 31 May 2026 and VOO's 30 June 2026 N-PORT filings.
- Holdings: 3,185 vs 501 in those filings. FSKAX's 2,687 extra names were 11.0% of the fund.
- Returns to 30 September 2026: VOO ahead by 0.42, 0.50, 1.16 and 0.60 points a year over 1, 3, 5 and 10 years.
- Taxes: about even. Over ten years to 31 December 2025, taxes on distributions cost FSKAX 0.48 points a year and VOO 0.46, per their prospectuses. Neither paid a capital gain distribution in its last five fiscal years.
- Wrapper: FSKAX is a mutual fund priced once a day; VOO is an ETF that trades all day at any broker.
How Much of FSKAX Is Already VOO
Nearly every VOO stock is in FSKAX, and at similar weights. FSKAX simply adds a long tail of smaller companies on top.
| Portfolios in the latest N-PORT filings | FSKAX (31 May 2026) | VOO (30 Jun 2026) |
|---|---|---|
| Holdings in the filing | 3,185 | 501 |
| Held by both funds | 498 | 498 |
| Share of the fund in those shared holdings | 88.9% | 99.6% |
| Holdings the other fund did not own | 2,687 (11.0% of FSKAX) | 3 (0.2% of VOO) |
| Top-10 weight | 36.0% | 37.9% |
| Overlap, sum of the smaller weight in each shared stock | 87.8% | |
The biggest names line up closely: NVIDIA 7.00% of FSKAX and 7.51% of VOO, Apple 6.25% and 6.59%, Microsoft 4.56% and 4.30%, Amazon 3.61% and 3.62%. FSKAX's extra 2,687 companies average about 0.004% each. The largest of them were names such as Snowflake and Cloudflare at around 0.1%.
So the honest description is that FSKAX is about 89% an S&P 500 fund with an 11% small and mid-cap sleeve attached. If you already own VOO, adding FSKAX buys you that sleeve and a lot of duplication.
FSKAX vs VOO Side by Side
| FSKAX | VOO | |
|---|---|---|
| Full name | Fidelity Total Market Index Fund | Vanguard S&P 500 ETF |
| Index | Dow Jones U.S. Total Stock Market Index (about 5,000 stocks) | S&P 500 Index |
| Method | Statistical sampling (sub-advised by Geode Capital Management) | Replication |
| Expense ratio | 0.015% | 0.03% |
| Holdings (N-PORT) | 3,185 (31 May 2026) | 501 (30 Jun 2026) |
| Information technology | 30.8% (28 Feb 2026) | 34.4% (31 Dec 2025) |
| Industrials | 10.6% | 8.2% |
| Portfolio turnover, latest fiscal year | 3% | 2% |
| Fund size | $124.7 billion (28 Feb 2026) | $1.48 trillion all share classes; $839 billion ETF class (31 Dec 2025) |
| Fund type | Mutual fund, priced once a day at NAV | ETF, trades all day at market price |
| Minimum | None | None set by Vanguard |
FSKAX is not a ZERO fund. Unlike FZROX, FSKAX's prospectus carries no "Fidelity brokerage account only" rule. It says you can buy "through a Fidelity® brokerage or mutual fund account, through a retirement account, or through an investment professional." Other brokers set their own terms for Fidelity mutual funds, including any transaction fee, so check yours. If portability is the worry with FZROX, FSKAX is Fidelity's answer; see FSKAX vs FZROX.
Ten Years of Returns
| Average annual return to 30 Sep 2026 | 1 year | 3 years | 5 years | 10 years |
|---|---|---|---|---|
| FSKAX | 15.28% | 22.35% | 12.59% | 14.69% |
| Dow Jones U.S. Total Stock Market Index | 15.28 | 22.34 | 12.58 | 14.68 |
| VOO (NAV) | 15.70% | 22.85% | 13.75% | 15.29% |
| S&P 500 | 15.74 | 22.89 | 13.79 | 15.33 |
| FSKAX minus VOO | -0.42 | -0.50 | -1.16 | -0.60 |
Both funds tracked their own index almost exactly. FSKAX was within 0.01 points a year of its index on every horizon, and VOO trailed the S&P 500 by roughly its fee. The whole gap between them is the market: large US companies beat small and mid-sized ones over all four windows.
| Hypothetical $10,000 held 10 years | Ending value |
|---|---|
| At FSKAX's 10-year return (14.69%) | $39,378 |
| At VOO's 10-year return (15.29%) | $41,487 |
That is a meaningful difference, and it would have been the other way round in a decade when small companies outperformed. Choosing VOO over FSKAX is choosing to skip the smaller 11% of the market. Choosing FSKAX is choosing not to make that call. Neither choice is a mistake; just know which one you are making.
This is educational information, not personalized investment advice. Past performance does not guarantee future results, and all investing carries the risk of loss.
Taxes: Closer Than the Wrapper Suggests
ETFs are often called more tax-efficient than mutual funds, because they can meet redemptions by handing over shares in kind instead of selling them. For these two particular funds the filings show very little difference, at least so far.
| Periods ended 31 Dec 2025 | 5 years before tax | 5 years after tax on distributions | 10 years before tax | 10 years after tax on distributions |
|---|---|---|---|---|
| FSKAX | 13.09% | 12.73% | 14.23% | 13.75% |
| VOO (NAV) | 14.38% | 13.99% | 14.78% | 14.32% |
| Lost to taxes each year | FSKAX 0.36 · VOO 0.39 | FSKAX 0.48 · VOO 0.46 | ||
The reason is in the annual reports. In FSKAX's five fiscal years to February 2026 its only distributions were from net investment income, meaning dividends; there was no capital gain distribution. VOO's ETF shares likewise paid no capital gains in 2021 through 2025. What you pay tax on with either fund is mostly the dividend, and the dividends are similar. A large, low-turnover index mutual fund can stay as clean as an ETF, though the ETF structure gives VOO a better tool for staying that way if heavy redemptions ever force sales.
Which One Fits You
Fidelity 401(k) or IRA with automatic contributions: FSKAX. It costs half as much, buys exact dollar amounts at the day's NAV, and covers the whole market in one holding. If your 401(k) menu offers FSKAX but not an S&P 500 ETF, the decision is already made for you, and it is a good one.
Account at Vanguard, Schwab or anywhere else: VOO. It trades at every broker with no special terms. Buying FSKAX away from Fidelity may carry a transaction fee, and if you want the whole market there, a total-market ETF such as VTI does the same job; see FSKAX vs VTI.
You want large caps only: VOO. Or FXAIX at Fidelity, which tracks the same S&P 500 for 0.015% (FXAIX vs VOO).
You want the whole market and might change brokers: FSKAX is fine at Fidelity, and a total-market ETF is the most portable option of all. FSKAX does not carry the Fidelity-only rule the ZERO funds have.
Taxable account: either works on the evidence above. VOO's ETF structure is the safer long-run bet for tax efficiency; FSKAX has matched it so far.
Do not hold both expecting to diversify. 99.6% of VOO is already in FSKAX.
Sources & Methodology
- FSKAX summary prospectus, 29 April 2026: fee table, index, method, turnover, after-tax returns, purchase rules.
- Fidelity Concord Street Trust Form N-CSR, year ended 28 February 2026: fund size, sectors, distributions.
- VOO summary prospectus, 28 April 2026: fee table, index, turnover, after-tax returns.
- Vanguard Index Funds Form N-CSR, year ended 31 December 2025: fund size, sectors, distributions.
- FSKAX Form N-PORT, 31 May 2026 and Vanguard 500 Index Fund Form N-PORT, 30 June 2026: holdings behind the overlap figures.
- Fidelity FSKAX performance page and Vanguard VOO profile page: returns to 30 September 2026.
How the overlap was computed. For each stock both funds held we took the smaller of its two weights and summed them, using the same N-PORT data as the Portfolio Overlap Checker. Fidelity's annual report counts 3,774 holdings at 28 February 2026; we use the N-PORT count so the page matches the tool.
This article is for general education and is not investment, tax or legal advice. Past performance does not guarantee future results, and all investing carries the risk of loss. Figures were checked against the sources above on 5 October 2026; confirm current details with Fidelity or Vanguard before acting.
FAQ: FSKAX vs VOO
Is FSKAX or VOO better?
Neither overall. FSKAX is cheaper (0.015% vs 0.03%) and owns the entire US market; VOO owns the S&P 500 and trades at any broker. VOO returned 15.29% a year over the ten years to 30 September 2026 against 14.69% for FSKAX, because large caps outperformed.
How much do FSKAX and VOO overlap?
87.8% by weight in their May and June 2026 SEC filings. 99.6% of VOO's assets were in stocks FSKAX also held.
Should I hold both FSKAX and VOO?
Usually not. Holding both duplicates almost all of VOO and adds extra large-cap weight. Pick the exposure you want: whole market (FSKAX) or large caps (VOO).
Is FSKAX the same as VTI?
Close but not identical. FSKAX tracks the Dow Jones U.S. Total Stock Market Index; VTI tracks a different total-market index. Both cover large, mid and small US stocks. See FSKAX vs VTI.
Can I buy FSKAX outside Fidelity?
Its prospectus does not restrict it to Fidelity brokerage accounts the way the ZERO funds are restricted. Whether another broker offers it, and at what transaction fee, is up to that broker.
Which is more tax-efficient?
On the record, they are close. Taxes on distributions cost FSKAX 0.48 points a year and VOO 0.46 over the ten years to 2025, per the prospectuses, and neither paid a capital gain distribution in the last five fiscal years.
Does FSKAX have a minimum investment?
No. Its prospectus says "There is no purchase minimum for fund shares."
Cite This Page
Journalists, educators and bloggers are welcome to cite this comparison. Please link back so readers can reach the underlying filings.
"FSKAX vs VOO: 88% Overlap, So You Are Really Choosing Total Market or the S&P 500." Wealthy Pot, 2026. https://wealthypot.com/fskax-vs-voo/
Related comparisons: FSKAX vs FZROX · FSKAX vs FXAIX · FSKAX vs VTI · FZROX vs VOO · FXAIX vs VOO · All ETF comparisons
