This paper presents a methodology to quantify the benefit of the distribution transformer life extension brought about by customer-owned distributed-generation (DG) units. The proposed methodology is applied to a realistic distribution system with various scenarios, including different penetration levels and combinations of the DG technologies. A number of realistic distribution transformers are then used to demonstrate the results. The results show the distribution transformer loss-of-life variation, as a function of the DG penetration level, presenting a monotonically decreasing characteristic which saturates after a certain penetration level. Regarding DG technologies, it should be noted that remarkable reduction is achieved in loss-of-life rates of the examined transformers for all of the proposed scenarios. However, the extent of the reduction largely depends on the production pattern of the DG unit. As revealed by the results, the microturbine emerges as the most promising technology in the life extension of distribution transformers.