Record Megacap 'Fragility' Puts S&P Rally At Risk

Rising instability among some of the biggest US stocks is driving a measure of single-stock “fragility” to record levels, with the market increasingly vulnerable to whipsaw patterns among clusters of shares such as occurred in the dot-com bubble of the late 1990s.

Stock fragility, a measure of a company’s daily share-price move relative to its recent volatility, is on track to reach its highest in more than 30 years among the largest 50 stocks in the S&P 500 Index, based on the average magnitude and frequency of such individual shocks so far in 2025, according to Bank of America Corp. strategists.

That’s as far back as their research goes, and covers not just the internet boom but also Russia’s default and the Asian financial crisis earlier in the ‘90s. The increasing jitters among single stocks flashes a potential warning for the broader market even as stock indexes hover near records — and combined with tariff and interest-rate concerns adds to a potentially worrisome mix.