Margin debt, the money investors borrow to buy stocks, has surged more than 53% over the past year, a rare spike that has historically preceded market downturns. According to FINRA data, this is only the 10th time in history that borrowing has climbed more than 50% in a single year. In eight of the nine previous instances, the S&P 500 was lower 12 months later, with the only exception being the post-COVID rebound in 2021. The spikes occurred before the dot-com crash of 2000 and the 2008 financial crisis, though the pattern does not guarantee a crash or predict its timing. Analysts suggest investors use this as an opportunity to review their portfolios for quality, diversified holdings rather than attempting to time the market.