The aim of this study was to present research results on the durability of projects in the context of EU and national regulations in force both in the financial perspectives for 2014–2020 and 2021–2027. In both analysed programming periods, the legal basis for the principle of durability is provided by EU regulations, i.e. Art. 71 of Regulation 1303/2013 and Art. 65 of Regulation 2021/1060. The main disadvantage of these regulations is the use of a phrase that allows for a violation of the principle of durability in a situation where a change that significantly affects the nature, objectives or conditions of implementation of the project may lead to a violation of the original objectives of the project. The consequence of this construction of the provisions referred to is the possibility of assigning full responsibility to the beneficiaries for failure to maintain the durability period in the event of only a probability that such a change actually occurred. In its jurisprudence, the Supreme Administrative Court expressed the view that in certain situations resulting in a violation of the principle of durability, the refund of a specific amount of project funding from EU funds should be waived.