The S&P 500 lost approximately 48% during the 1973–1974 stock-market crash.
The decline lasted from January 11, 1973, until October 3, 1974. The market fell amid high inflation, economic stagnation, the 1973 oil crisis, rising energy prices, and political uncertainty connected to the Watergate scandal and President Richard Nixon's resignation.
The 48% figure describes the S&P 500's fall from its 1973 peak to its 1974 low. Other indexes and individual shares experienced different losses, so the percentage is an index-specific historical measure rather than a claim that every stock fell by exactly that amount.
This crash is often discussed alongside the 1970s “stagflation” era. It was part of a prolonged bear market, not a single trading-day collapse like Black Monday in 1987.