Firm Expansion and Stock Price Momentum

We document a significant and robust connection between firm-level asset changes and return momentum. Momentum profits are large and significant for firms that have experienced large asset expansions or contractions, whereas they otherwise are small and often insignificant. The interaction pattern is not subsumed by previously documented drivers of momentum and shows up in market states where prior literature has documented an absence of momentum profits. Furthermore, we find a positive time series relationship between aggregate asset growth (AG) and return momentum, and the effect of aggregate AG is stronger than that of variables related to business cycles and investor sentiment. While most existing models of firm investment and momentum cannot explain our results, recent real options models appear to hold the most promise.