Tools to estimate survival, such as ePrognosis , were developed for general, not cancer, populations. In older patients with breast cancer, accurate overall survival estimates would facilitate discussions about adjuvant therapies. Secondary analyses were performed of data from two parallel breast cancer studies (CALGB/Alliance 49907/NCT000224102 and CALGB/Alliance 369901/NCT00068328). We included patients (n = 971) who were age 70 years and older with complete baseline quality of life data (194 from 49907; 777 from 369901). Estimated versus observed all-cause two-year mortality rates were compared. ePrognosis score was calculated based on age, sex, and daily function (derived from EORTC QLQ-C30). ePrognosis scores range from 0 to 10, with higher scores indicating worse prognosis based on mortality of community-dwelling elders and were categorized into three groups (0-2, 3-6, 7-10). Observed mortality rates were estimated using Kaplan-Meier methods. Patient mean age was 75.8 years (range 70-91) and 73% had stage I-IIA disease. Most patients were classified by ePrognosis as good prognosis (n = 562, 58% 0-2) and few (n = 18, 2% 7-10) poor prognosis. Two-year observed mortality rates were significantly lower than ePrognosis estimates for patients scoring 0-2 (2% vs 5%, p = 0.001) and 3-6 (8% vs 12%, p = 0.01). The same trend was seen with scores of 7-10 (23% vs 36%, p = 0.25). ePrognosis tool only modestly overestimates mortality rate in older breast cancer patients enrolled in two cooperative group studies. This tool, which estimates non-cancer mortality risk based on readily available clinical information may inform adjuvant therapy decisions but should be validated in non-clinical trial populations.