7 stocks control more than 25% of Vanguard Total Stock Market Index Fund

For decades, the standard advice from index investors has been simple: Buy the entire market, put it on autopilot, and reap the benefits of instant diversification.

flagship Vanguard Morningstar Total Stock Market Index Fund (Available in ETF form VTI or mutual funds VTSAX, (plus other mutual fund share classes) are often hailed as the gold standard of “set it and forget it” investing.

The firm holds more than 3,500 U.S. stocks and is involved in every corner of the U.S. stock market, from multi-trillion dollar technology giants to tiny startups.

However, a quick look behind the scenes reveals a stark reality: Just seven large technology companies account for more than 25% of the entire fund’s value.

If a handful of large companies control a quarter of the “total market” funds, are investors gaining true diversification, or are they taking on hidden concentration risk?

Tech giants’ footprint in broad market index funds hits record high

Because VTI and VTSAX are market capitalization weighted, a company’s influence on the fund is directly related to its market valuation. As corporate giants continue to grow in size, their footprint in broad market index funds has reached an all-time high.

The top seven holdings combined accounted for 29.48% of the fund’s total assets as of September 30, 2026, according to Morningstar. These include six so-called “Magnificent 7” large technology stocks, as well as Broadcom.

While there are approximately 3,500 stocks remaining, their collective moves are often overshadowed by the top heavyweights.

When big tech stocks rise, total market capital surges. But when the tech sector struggles, even thousands of smaller holdings can’t stop the broader index from taking a hit.

Investors must understand what is included in their ETF and mutual fund investments to help them build a properly diversified portfolio.

Is Concentrated Risk Really a Threat?

Market concentration is not inherently a bad thing. In fact, the top-heavy weighting of giant tech companies has been the primary growth engine driving benchmark index returns over the past few years.

However, high concentration creates two main challenges for investors:

1. Industry overlap in the portfolio

If you hold a stock market fund along with an S&P 500 ETF, Nasdaq 100 ETF, or growth fund, you may have less exposure to a diverse group of companies than you realize. All four funds have nearly identical top holdings.

2. The illusion of small and mid-cap exposure

While VTI technically holds small and mid-cap stocks, their total weighting is smaller compared to large-cap stocks. Large-cap stocks account for about 70% of the entire fund’s weighting, which means that price fluctuations in small and mid-cap stocks have a minimal impact on the fund’s overall performance.

What Vanguard thinks of “Mag 7”

Interestingly, Vanguard’s own research suggests that the concentration argument may be a bit too simplistic.

Vanguard analysis pointed out that although Magnificent 7 is often classified under the “big technology” label, their basic revenue sources are completely different. For example:

• Microsoft Generate revenue from enterprise cloud infrastructure, software and personal computing.
• Amazon Generate revenue through e-commerce, cloud computing (AWS) and digital advertising.
• Tesla Mainly engaged in consumer electric vehicles and energy storage business.
• yuan and alphabet Rely heavily on digital advertising.

Because their business models, customer bases and risk factors vary, these companies don’t always move in lockstep.

From Vanguard’s perspective, owning these giants still allows for diversification in the global economy.

3 ways to rebalance risk exposure

If you’re concerned about market concentration in core equity, you don’t need to abandon index funds entirely.

Consider these three adjustments to manage your risk:

1. Included in equal-weighted index funds: Unlike market-cap-weighted funds, equal-weighted ETFs (such as the Invesco S&P 500 Equal-Weight ETF, RSP) provide the same allocation to every stock in the index. This removes the dominance of megacap stocks and tilts your portfolio toward value and mid-cap stocks.
2. Adding targeted small-cap and international allocations: To give small companies a real say in your portfolio, consider pairing VTI with a dedicated small-cap ETF (like the Vanguard Small-Cap ETF, VB) or expanding your international stock footprint (through a fund like VXUS).
3. Reevaluate your overall technology exposure: Take inventory of all funds in your workplace 401(k) and taxable brokerage accounts. If you hold both an industry-specific technology fund and a market-wide fund, you may be taking on more concentration risk than expected.

Know what’s in your portfolio

Vanguard’s Total Stock Market Index Fund remains one of the most efficient, low-cost vehicles for creating wealth. However, holding thousands of stocks does not protect a fund from top-heavy concentration.

Understanding what you own — and how much of it is covered by a few large-cap stocks — is key to building a resilient portfolio.

Related: Vanguard’s S&P 500 index fund’s dividend growth outpaces its own growth