A large and growing percentage of prostate cancers are diagnosed among men of advanced age. Current guidelines stratify treatment recommendations based on life expectancy; therefore, accurate determination of life expectancy is essential. Evidence shows that patient-related factors, including age, comorbidities, and functional status, are critical determinants of life expectancy. Equally strong evidence supports tumor-related factors, including Gleason score, tumor stage, and prostate-specific antigen, and efficacy of treatment. Currently, no available tools comprehensively consider all pertinent factors in determining life expectancy.