In colombia, distribution transformer ratings are selected upon the rated current flowing through circuits and branches feeding low-voltage networks. As a result, transformers turn out oversized. This paper shows a methodology for selecting distribution transformers based on technical and technoeconomical criteria as an alternative to current methodologies complying with NTC 2050. Whereas, technical criteria assure the operation of transformer within its maximum efficiency without loss of shelf life, the technoeconomical criteria balance a reasonable reduction of shelf life with a lower investment and service cost, even though the transformer is operating out of its maximun efficiency point. As a matter of fact, this later approach is of bigger interest for power distribution utilities. The proposed methodology, added to the overload capability of the transformers, allow to find the most suitable ratings in order to supply the expected demand, with lower investment and service costs and higher efficiency through the assets shelf life.