In this paper, we analyze the impact of a low interest rate environment on banks’ risk-weighted assets (RWA)/total assets ratio, also known as RWA density. In theory, a low RWA density can imply a bank´s lower risk, lower capital require­ments and, therefore, a higher return on average equity (ROAE), implying a bank’s higher competitiveness. In the theoretical part, we identify the key factors affecting RWA variability, which is correlated with RWA density. In the empirical part, based on a sample of 352 banks from the Eurozone, Japan, Sweden, Switzer­land and Denmark during the period 2011–2017, we apply the system of the Generalized Method of Moments. We did not find any evidence to support the main hypothesis that a low interest rate environment will influence banks’ RWA density after 1 year. We rejected our hypothesis even for periods of 2 and 3 years. Our contribution to the literature is three-fold. Firstly, we discuss the theoretical and practical aspects of RWA variability and density. Secondly, unlike other researchers, we also focus on macro-level determinants (including a low interest rate environment), and identify ROAE and bank heterogeneity as significant determinants of RWA density. Finally, we examine a large data sample, which enables us to identify the key determinants of RWA density and to obtain robust results from across different regions and bank business models in the recent period. Our findings survive a battery of robustness checks and provide some solid support for regulators when they propose new bank capital requirements and reform the calculation of RWA.