Although the degree-day method for heating is classified as a single-parameter method, as it only accounts for daily changes in outdoor air temperature to estimate the heating demand of a building due to climatic influences, it has proven to be highly reliable over decades of practice and is now widely regarded as a standard method for determining heating requirements. However, due to evident climate changes and rising outdoor air temperatures, treating the heating degree days as a prescribed constant value for the specified location, leads to significantly inaccurate results, as demonstrated in this paper through an analysis of data from the Republic Hydrometeorological Service. Meanwhile, the use of the cooling degree days method to determine cooling demand has proven to be highly unreliable. This is because the method does not account for solar radiation, which, during the summer months, is as significant a factor as outdoor air temperature. To address this issue, while preserving the core concept of the method the heat load to be removed from a cooled space is proportional to the difference between the average daily outdoor air temperature and the base indoor temperature, a considerably lower base indoor temperature can be used in place of the internal design (reference) temperature. This paper presents the corrected method, along with international experiences and best practices, and includes data from the Republic Hydrometeorological Service. Additionally, cooling degree days for Belgrade have been calculated and presented, providing more accurate and reliable cooling demand forecasts.