Why do corporations accumulate liquid assets? We show theoretically that intertemporal trade-offs between interest income taxation and the cost of external finance determine optimal savings. Intriguingly, we find that, controlling for Tobin's q, saving and cash flow are negatively related because firms lower cash reserves to invest after receiving positive cash-flow shocks, and vice versa. Consistent with theory, we estimate negative propensities to save out of cash flow. We also find that income uncertainty affects saving more than do external finance constraints. Therefore, contrary to previous evidence, saving propensities reflect too many forces to be used to measure external finance constraints.

Why do corporations accumulate liquid assets? We show theoretically that intertemporal trade‐offs between interest income taxation and the cost of external finance determine optimal savings. Intriguingly, we find that, controlling for Tobin's q , saving and cash flow are negatively related because firms lower cash reserves to invest after receiving positive cash‐flow shocks, and vice versa. Consistent with theory, we estimate negative propensities to save out of cash flow. We also find that income uncertainty affects saving more than do external finance constraints. Therefore, contrary to previous evidence, saving propensities reflect too many forces to be used to measure external finance constraints.

We derive and test q-theory implications for cross-sectional stock returns. Under constant returns to scale, stock returns equal levered investment returns, which are tied directly to firm characteristics. When we use generalized method of moments to match average levered investment returns to average observed stock returns, the model captures the average stock returns of portfolios sorted by earnings surprises, book-to-market equity, and capital investment. When we try to match expected returns and return variances simultaneously, the variances predicted in the model are largely comparable to those observed in the data. However, the resulting expected return errors are large.