What Is IVOO? Vanguard S&P Mid-Cap 400 Index Fund ETF Shares

Most people treat mid-cap indexes as interchangeable, but the S&P 400 and the Russell Midcap universe are built on different principles. Russell ranks by size and includes whatever falls in the range. S&P uses a committee that applies additional criteria, including a requirement for positive earnings in the most recent quarter and over the trailing year before a company is added.

That single rule changes the population. Companies that have never made money, common in biotechnology and in recently listed technology, are not eligible for the S&P 400 no matter their market value. Over long periods this profitability filter has been studied as a source of difference between the two families of index, though how much it contributes varies by period and is not something any fund can promise.

The committee also means membership is not purely mechanical. Additions and deletions happen through the year rather than at one annual reconstitution, which spreads turnover out instead of concentrating it on a single, heavily traded date.

Approximate weights as of August 2026; refresh quarterly from Vanguard's fund page. Each ticker links to its individual stock guide in Walnut.

No position reaches 1%. Twilio is the largest at 0.9%, followed by Carpenter Technology, MKS, Curtiss-Wright and Entegris in the 0.7% to 0.8% range. With 400 constituents and no dominant company, individual holdings simply cannot drive the fund, so what matters is sector and factor exposure.

Industrials at 25% is the defining weight, well above the broad US market, and it arrives through specialised manufacturers: Curtiss-Wright in aerospace components, nVent in electrical connection, Sterling Infrastructure in construction, ATI and Carpenter Technology in specialty metals. These are businesses tied to industrial capital spending rather than to consumer sentiment.

The list also illustrates how companies arrive in a mid-cap index. Twilio and Illumina were both far larger businesses by market value a few years ago. A mid-cap index is not only a collection of growing small companies; it is equally a collection of large companies that have shrunk into the range.

IVOO is not the largest fund on this index. Two considerably bigger ETFs track the same S&P MidCap 400, and one of them charges slightly less. In practice all three deliver near-identical exposure, and the tie-breakers are the bid-ask spread, which is wider on smaller funds, and which brokerage platform an investor already uses.

The strategic question is whether a dedicated mid-cap holding is needed at all. A US total-market fund already includes the entire S&P 400 at its natural weight, so adding IVOO is a deliberate overweight to the middle of the market. That case is usually made on the argument that the S&P 500 has become dominated by a handful of very large companies and that mid-caps offer exposure to a different part of the economy.

It is a poor substitute for small-cap exposure, since the S&P 400 sits well above that range, and the 1.16% yield puts it outside income use. What it does provide, cheaply, is a broad and unusually flat slice of profitable mid-sized American companies.

There are three common ways to get IVOO exposure. Buy shares (or fractional shares) of IVOO directly at any major broker that lists it. Hold it as a core position and layer more concentrated ideas on top. Or build it into a thematic portfolio in Walnut, so IVOO sits alongside other holdings that express the same thesis, with target weights you can rebalance toward. IVOO trades like a stock during market hours, so you buy it the same way you would any listed share.

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Whether IVOO is a good buy depends less on any single call and more on your time horizon and what you already hold: it tracks the S&P MidCap 400 Index, so the real question is whether you want that exposure in your mix and at what weight. We walk through valuation, concentration, and what would have to be true for it to outperform from here in is IVOO a buy?

IVOO gives you the S&P MidCap 400 Index exposure in one ticker at a 0.07% expense ratio. Most investors use it as a core holding and layer more concentrated thematic portfolios on top.

Whether IVOO is worth buying today depends more on your time horizon and what you already hold than on any single call. We walk through valuation, concentration, and what would have to be true for it to outperform from here in is IVOO a buy?

IVOO yields 1.16% as of August 2026, paid by passing through the dividends of its underlying holdings. For the payout schedule, history, and how the distributions are taxed, see IVOO dividend: yield and schedule.

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