Our study uses a new business cycle (BC) index and a nonlinear panel smooth transition regression model on quarterly data of 1538 bank holding companies of the United States to investigate response of capital adequacy ratios (CARs) to changes in economic activity. Our findings confirm the existence of nonlinear effects of BC on CARs. Although we use a nonlinear model and a new proxy of BC, our results about CARs are not only consistent with existing mainstream literature but also improve estimation and goodness of the estimation of CARs. The study outcome is useful for policymakers for CARs' standards adjustments during recessions.