R&D tax deductions constitute an interesting way how to reduce income tax for taxpayers carrying out research and development activities. Despite the fact that the calculation of such deduction itself is not too complicated, claiming the deduction in tax declarations duly and properly can become tricky. Besides the legislation, the conditions are affected significantly by the judicial decisions made by the Supreme Administrative Court. Last but not least, even the practices of the Czech Financial Administration during tax inspections play a major role.