This paper estimates the effects of tax incentives on charitable contributions in the UK, using the universe of self-assessment income tax returns between 2005 and 2013. We exploit variation from a large reform in 2010 to estimate intensive- and extensive-margin tax-price elasticities of giving. Using a predicted-tax-rate instrument for the price of giving relative to consumption, we find an intensive-margin elasticity of about -0.2 and an extensive-margin elasticity of -0.1, yielding a total elasticity of about -0.3. To further explore the extensive-margin response, we propose a model with a fixed cost of declaring donations and obtain a structural estimate of that cost of around 47 pound. We also study the welfare effects of tax incentives, extending the theoretical literature to allow for extensive-margin giving and for a fixed cost of declaring donations. Taking into account these factors, there is a case for increasing the subsidy on charitable giving in the UK. (C) 2019 Published by Elsevier B.V.