In the 2008 crash, the S&P 500 lost 38.5% during the calendar year.
The decline made 2008 one of the worst years in the index’s history. The S&P 500 tracks large U.S. companies, so its performance reflected widespread damage to financial institutions, industrial firms, consumer businesses, and other sectors during the global crisis.
The annual fall came as losses from U.S. housing and mortgage markets spread through the financial system. Lehman Brothers filed for bankruptcy in September, while governments and central banks introduced emergency measures to support banks, credit markets, and economic activity.
The 38.5% figure is a calendar-year total return comparison often cited for the price index, not a description of the largest single-day move. The market continued falling into early 2009 before reaching its crisis low in March of that year.