Wealthy PotVO vs VOO: Mid Caps or the S&P 500, and Most of VO Is Already in VOO
VO and VOO are both Vanguard index ETFs that charge 0.03%, but they hold different slices of the US market. VO, now called the Vanguard Morningstar Mid-Cap ETF, holds about 280 mid-sized companies. VOO holds the S&P 500. Their overlap is only 16.4%, yet 91.1% of VO's money sits in companies that are also in the S&P 500. The S&P 500 includes many companies that are mid-sized by Morningstar's measure, but VOO holds them at small weights next to giants such as NVIDIA and Apple. Over the ten years to 30 September 2026, VOO returned 15.29% a year and VO 10.96%. VOO is the core holding for most people. VO is an add-on for those who want more weight in mid-sized companies.
Table of Contents
The Short Answer
- Fees: a tie at 0.03%. VO's fee was cut from 0.04% after 2025; its April 2026 prospectus shows 0.03%, the same as VOO.
- Overlap: 16.4%. But it runs one way: 91.1% of VO's weight is in companies VOO holds, while only 16.4% of VOO's weight is in companies VO holds. Both filings are dated 30 June 2026.
- Holdings: 280 vs 505. Median company size: $51.2 billion in VO, $436.0 billion in VOO (Vanguard, 31 August 2026).
- Concentration: top ten 9.5% vs 37.9% of each fund at 30 June 2026. VO spreads its money much more evenly.
- Returns to 30 September 2026 (NAV): VOO 15.29% a year over ten years, VO 10.96%. VOO was ahead over one, three and five years too.
- Volatility: VO a bit higher. Three-year standard deviation 14.34% vs 13.06% at 30 June 2026.
- Complements, not substitutes. Holding both adds mid-cap weight; it is not a doubling-up.
The Overlap Is Lopsided
We matched the SEC portfolio filings for the Vanguard Mid-Cap Index Fund (VO's fund) and the Vanguard 500 Index Fund (VOO's fund), both for the period ended 30 June 2026.
| SEC portfolio filings, 30 June 2026 | VO | VOO |
|---|---|---|
| Holdings in the filing | 279 | 501 |
| Held by both funds | 247 | 247 |
| Share of the fund in those shared holdings | 91.1% | 16.4% |
| Holdings the other fund did not own | 32 (8.6% of VO) | 254 (83.3% of VOO) |
| Overlap, sum of the smaller weight in each shared stock | 16.4% | |
Same companies, very different weights. VO's largest positions are S&P 500 members, but they are small parts of VOO. Vertiv was 1.22% of VO and 0.20% of VOO. Western Digital was 1.06% and 0.34%, Seagate 1.05% and 0.34%, Quanta Services and Howmet Aerospace about 1.04% of VO and 0.17% of VOO. That is why a fund can be 91% inside the S&P 500 by company while sharing only 16% of its money.
What VOO has that VO does not: the very largest companies. The 254 VOO-only holdings were 83.3% of VOO, led by NVIDIA (7.51%), Apple (6.59%), Alphabet (5.84%), Microsoft (4.30%), Amazon (3.62%) and Broadcom (2.77%). None of those is mid-sized.
What VO has that VOO does not: 32 mid-sized companies outside the S&P 500, 8.6% of VO. The largest were Bloom Energy (0.79%), Cloudflare (0.76%), Rocket Lab (0.57%), Cheniere Energy (0.48%), Ferguson Enterprises (0.45%) and Waste Connections (0.41%).
VO vs VOO Side by Side
| VO | VOO | |
|---|---|---|
| Full name (from 29 Jul 2026) | Vanguard Morningstar Mid-Cap ETF | Vanguard S&P 500 ETF |
| Index | Morningstar US Mid Cap Index (CRSP US Mid Cap Index until 29 Jul 2026) | S&P 500 |
| Expense ratio | 0.03% | 0.03% |
| Prospectus cost on $10,000, 10 years | $39 | $39 |
| Number of stocks | 280 (31 Aug 2026) | 505 (31 Aug 2026) |
| Median market cap | $51.2bn | $436.0bn |
| Top ten holdings (30 Jun 2026) | 9.5% | 37.9% |
| Largest sector (30 Jun 2026) | Industrials 21.4% (ICB) | Information Technology 38.0% (GICS) |
| 3-year standard deviation (30 Jun 2026) | 14.34% | 13.06% |
| Turnover (latest fiscal year) | 16% | 2% |
| Assets (31 Aug 2026) | ETF class $107.4bn; fund $226.4bn | ETF class $1.0 trillion; fund $1.8 trillion |
| Inception | 26 Jan 2004 | 7 Sep 2010 |
| 10-year return, NAV, to 30 Sep 2026 | 10.96% | 15.29% |
VO's turnover is higher, likely because a mid-cap index has two edges: companies that grow too big move up to large caps, and those that shrink move down. Even so, 16% is low, and the prospectuses' after-tax figures show similar tax drag for both funds. Over ten years to 2025, returns after taxes on distributions were 0.44 points a year below pre-tax returns for VO and 0.46 points for VOO.
Returns: Large Caps Won the Decade
| Average annual, NAV, to 30 Sep 2026 | 1 year | 3 years | 5 years | 10 years |
|---|---|---|---|---|
| VO | 8.36% | 16.44% | 7.44% | 10.96% |
| Spliced Mid Cap Index | 8.38 | 16.46 | 7.45 | 10.97 |
| VOO | 15.70% | 22.85% | 13.75% | 15.29% |
| VOO minus VO | +7.34 | +6.41 | +6.31 | +4.33 |
Both funds tracked their indexes to within a few hundredths of a point. The gap between them is the gap between mid caps and the S&P 500, and over every window here it favored the S&P 500 by a wide margin. VOO's largest holdings, the very biggest technology companies, are exactly the stocks VO does not own. Their run is the main story of the last decade. We draw that link from the holdings; Vanguard's documents do not attribute it.
The earlier quarter told the same story: to 30 June 2026, VO returned 11.78% a year over ten years and VOO 15.47%. The prospectuses, to 31 December 2025, show VO at 10.92% and VOO at 14.78%.
$10,000 at VOO's ten-year rate to 30 September 2026 would have grown to about $41,487; at VO's, about $28,292. (Hypothetical arithmetic on the published ten-year rates, ignoring taxes and trading costs. Not a forecast.) Nothing in either filing says which slice will lead next.
VO's New Name and Index
If VO looks different on your statement, that is why. Vanguard's supplement dated 29 July 2026 says Morningstar "has announced the acquisition of the Center for Research in Security Prices ("CRSP") and its CRSP Market Indexes." As a result, Vanguard Mid-Cap Index Fund became the Vanguard Morningstar Mid-Cap Index Fund, its ETF shares became the Vanguard Morningstar Mid-Cap ETF, and its index, the CRSP US Mid Cap Index, became the Morningstar US Mid Cap Index. All three changes took effect on 29 July 2026.
The supplement states that "Each Fund's investment objective, strategies, and polices remain unchanged." The ticker is still VO. The same renaming applied to VTI and several other Vanguard funds; VOO, which tracks the S&P 500, was not affected.
Which One Fits You
Building a simple core portfolio? VOO, or a total-market fund such as VTI. VO on its own leaves out the largest US companies entirely.
Already own VOO and want more in mid-sized companies? VO is the cleanest add-on at the same fee. Because the two share only 16.4% of their money, it changes your mix rather than duplicating it. Be aware that, by company, most of VO is already in VOO at small weights; you are raising their weight, not adding new names.
Want the whole market in one fund? A total-market fund holds both slices at market weight. See VTI vs VOO or ITOT vs VOO.
Retirement account or taxable? Both are low-turnover ETFs with similar after-tax drag in their prospectus tables, so either works in a taxable account. In a 401(k), use whatever S&P 500 or mid-cap index fund your plan offers; the index matters more than the ticker.
Comfort with swings? VO's prospectus notes that "historically small- and mid-cap stocks have typically been more volatile." Its three-year standard deviation was higher than VOO's at 30 June 2026, 14.34% against 13.06%.
This is educational information, not personalized investment advice. Past performance does not guarantee future results, and all investing carries the risk of loss.
Sources & Methodology
- VO summary prospectus, 28 April 2026: objective, index, fee table (restated to current fees), cost example, turnover, risk text, returns to 31 December 2025.
- VOO summary prospectus, 28 April 2026: index, fee, cost example, turnover, returns to 31 December 2025.
- Vanguard supplement dated 29 July 2026: the Morningstar rename of VO's fund, ETF and index.
- Vanguard Index Funds annual report, year ended 31 December 2025: VO's 0.04% cost in 2025 and the later fee reduction.
- VO fact sheet and VOO fact sheet, as of 30 June 2026: top ten, sectors, standard deviation, returns.
- Vanguard's VO profile and VOO profile: holdings, median market cap, assets, returns to 30 September 2026.
How the overlap was computed. Our Portfolio Overlap Checker reads each fund's Form N-PORT holdings and adds up the smaller of the two weights for every shared holding. Both filings are for the period ended 30 June 2026.
What we did not verify. We did not read Morningstar's or S&P's index rulebooks, so our explanation of why so many S&P 500 members count as mid caps is the plain reading of the holdings, not a quotation from either index provider.
This article is for general education and is not investment, tax or legal advice. Fund data changes daily, index returns cannot be invested in directly, and past performance does not guarantee future results. Figures were checked against the sources above on 5 October 2026; confirm current figures with Vanguard before acting.
FAQ: VO vs VOO
Is VO or VOO better?
They do different jobs. VOO holds the S&P 500 and suits most people as a core holding. VO holds about 280 mid-sized companies. Over the ten years to 30 September 2026, VOO returned 15.29% a year and VO 10.96%.
How much do VO and VOO overlap?
16.4%, from both funds' 30 June 2026 SEC filings. But 91.1% of VO's weight is in companies that are also in VOO, held there at much smaller weights.
Should I hold VO and VOO together?
You can, if you want more mid-cap weight than the S&P 500 gives you. It is a tilt, not a duplicate. A total-market fund is the simpler way to hold both slices at market weight.
What is VO's expense ratio?
0.03%, per its April 2026 prospectus, which restated the fee to reflect current costs. VO's ETF shares cost 0.04% during 2025.
Did VO change its name?
Yes. From 29 July 2026 it is the Vanguard Morningstar Mid-Cap ETF, and its index is the Morningstar US Mid Cap Index (formerly CRSP US Mid Cap). The ticker and strategy did not change.
Is VO more volatile than VOO?
Somewhat. Its three-year standard deviation was 14.34% at 30 June 2026, against 13.06% for VOO.
Does VO hold NVIDIA or Apple?
No. Neither appeared in VO's 30 June 2026 filing. The biggest US companies are large caps and sit in VOO, not in a mid-cap fund.
Cite This Page
Journalists, educators and bloggers are welcome to cite this comparison. Please link back so readers can reach the underlying filings.
"VO vs VOO: Mid Caps or the S&P 500, and Most of VO Is Already in VOO." Wealthy Pot, 2026. https://wealthypot.com/vo-vs-voo/
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