Tax expenditures (TEs) are used widely around the world. Their role in the fiscal systems of low- and middle-income countries has recently attracted increased scrutiny. At the heart of this scrutiny lies a desire to understand the extent of revenue foregone due to TEs, often in countries that have not undertaken such an exercise before. While a policy-maker preparing a TE report for the first time will likely find ample guidance on the broad principles (either with dedicated technical assistance or through ‘how-to’ literature), there are myriad practical, often country-specific hurdles to overcome when preparing estimates. This paper discusses the key steps and challenges in preparing a TE report. It draws where relevant from the authors’ experiences of supporting TE reporting in Rwanda and Uganda, two countries that have only recently begun the practice of regular TE reporting and have had fairly contrasting experiences.