A simplified second-degree expression is developed for the approximate estimation of annual heating degree-days to various base temperatures. The only data needed for the application of this relation is the degree-days value to some reference base temperature and the mean annual temperature of the location. No statistical analysis is required for the identification of the parameters of the suggested relation, and so it is location insensitive. The quadratic relation proved to be quite accurate when applied to data from many cities from Greece and other Countries. Apart from the estimation of heating degree-days, the suggested expression can be useful for analytical purposes. due to its explicit and simple form. (C) 2009 Elsevier Ltd. All rights reserved.