The Dow Jones Industrial Average fell about 89% from its 1929 peak to its 1932 low.
The index reached a pre-crash peak in September 1929 and then declined through the crash and the broader economic collapse. Its low came in July 1932, nearly three years after the first dramatic selling wave.
This figure describes the complete peak-to-trough decline, not the loss on a single day. The initial crash was followed by further failures, deflation, unemployment, bank problems, and weakened business activity. Those forces kept depressing share prices after the famous October sessions.
The Dow did not regain its September 1929 closing high until 1954. That long recovery period is one reason the episode is often remembered as more than a brief stock-market panic. The 89% figure is approximate because historical calculations can differ slightly depending on whether closing values or intraday levels are used.