The Tax Cuts and Jobs Act of 2017 (TCJA) introduced substantial changes to the U.S. corporate tax system, including a lower statutory tax rate and the adoption of a more territorial-like international tax framework. These shifts carry important implications for the complexity of corporate tax positions. We present a theoretical framework that models a firm’s choice regarding the complexity of tax positions. We then empirically test its predictions using measures of tax risk, uncertainty, and firm-level behavior before and after the TCJA. Our results suggest that the positive association between tax uncertainty and tax avoidance declines significantly after the TCJA, particularly for firms with tax haven subsidiaries. Contrary to recent claims that corporate tax complexity would persist or worsen without deliberate efforts to simplify the tax code, our findings suggest that policy interventions that reduce incentives for elaborate tax planning can meaningfully simplify corporate tax positions. This evidence provides insights for policymakers and stakeholders seeking to design more efficient and equitable tax systems.