An empirical equilibrium job search model with wage posting is developed to analyze the impact of U.K. tax reforms. The model allows for a rich characterization of the labor market, with hours responses, accurate representations of the tax and transfer system, and both worker and firm heterogeneity. The British Working Families' Tax Credit and contemporaneous reforms are predicted to increase employment, with equilibrium effects found to be relatively modest. The model is used to assess the impact of alternative policies, with equilibrium effects shown to become important as the generosity of tax credits is increased.