The anatomy of lost stock market decades

• U.S. markets alternate between multi-decade growth and lost periods. • Growth phases average 10 % annual returns; lost phases yield near zero. • Exponential-loss metric signals transitions between market regimes. • Lost periods often align with early-stage technological innovations. • Identifying market phase enhances long-term asset allocation strategies. This paper explores the existence and implications of long-term stock market cy- cles, characterized by alternating periods of growth and lost performance, in the U.S. and global markets. Using historical data spanning over 150 years, we define growth periods as intervals of sustained positive returns lasting ten years or more and lost periods as phases of near-zero returns lasting a decade or longer. Our findings confirm the persistence of these cycles in the U.S. market, with growth periods typically gen- erating an average annual return of 10 % and lost periods yielding zero returns. The implications for asset allocation are significant.