S&P 500 top 10 stocks reach 40% weight, fueling concentration risk

The S&P 500's top 10 stocks have swelled to roughly 40% of the index, a concentration level that is prompting investors to reconsider portfolio diversification strategies.

The top 10 holdings now command a share of the benchmark that exceeds historical averages, according to market data. Nvidia Corp., Apple Inc. and Microsoft Corp. lead the ranks, with Nvidia alone representing 13.1% of the Vanguard Growth ETF (VUG), per fund disclosures. Apple and Microsoft account for 12.3% and 9%, respectively. VUG, which tracks large-cap U.S. growth stocks, has $393.8 billion in assets under management and charges a 0.03% expense ratio.

The Vanguard FTSE Developed Markets ETF (VEFA) has emerged as one alternative for investors seeking to reduce single-market exposure. The fund tracks developed international equities with an analyst sentiment tilt, weighting holdings based on earnings revision trends rather than market capitalization alone. That methodology may help avoid the momentum-driven concentration that has pushed U.S. mega-cap valuations to elevated levels.

For portfolio managers, the risk is structural. A correction in any of the top-weighted mega-cap stocks would disproportionately drag the broader index. The narrow leadership means passive investors are effectively making a concentrated bet on a handful of companies, even while holding a product marketed as diversified.

VEFA's international focus provides a natural hedge. The fund holds stocks across developed markets including Japan, the United Kingdom and France. Its analyst sentiment methodology screens for companies with improving earnings revision trends, a factor that has historically added value in international equities where analyst coverage is less uniform than in the U.S.

The shift toward international diversification is already visible in fund flow data. Investors have been adding to international equity ETFs while U.S. large-cap growth funds have seen mixed inflows, according to industry data. If S&P 500 concentration continues to rise, that rotation could accelerate.

This article is for informational purposes only and does not constitute investment advice.