Background: Time to initiate breast cancer treatment is increasing in the United States, but controversy surrounds the impact of TTT on survival. The impact of the interval between diagnosis and treatment is a source of concern to patients and clinicians. We investigated the relationship using separate analyses of two of the largest cancer databases in the United States. Methods: Patients had noninflammatory, nonmetastatic, invasive breast cancer, with surgery as initial treatment. The first study used the SEER-Medicare database (SMDB), and second, the National Cancer Database (NCDB). Each analysis assessed survival as a function of time between diagnosis and operation ( ≤ 30, 31-60, 61-90, 91-120, and 121-180 days [d] from diagnosis), adjusting for demographics, comorbidities, tumor-related factors, and treatment. Results: The SMDB cohort had 94,544 patients ≥ 66 years old, diagnosed between 1992 and 2009. With each interval delay increase, adjusted overall survival (OS) was lower for all patients (hazard ratio [HR] 1.09, p< 0.001), and for those having stage I (hazard ratio [HR] 1.13, p< 0.001) and stage II (HR 1.06, p= 0.010) disease. Breast cancer-specific mortality increased with each 60-d interval (subhazard ratio 1.26, p= 0.03). The NCDB study evaluated 115,790 patients ≥ 18 years old, diagnosed between 2003 and 2005. The adjusted overall mortality HR was 1.10 (p< 0.001) for each increasing interval, significant in stages I (HR 1.16, p< 0.001) and II (1.09, p< 0.001) disease. Five-year OS adjusted for demographics, comorbidities, tumor-related factors and treatment in the SMDB progressively declined from 78.1% for ≤ 30 d to 60.9% for 121-180 d and in the NCDB from 88.0% for ≤ 30 d to 80.4% for 121-180 d. Conclusions: Independent analyses of two national cohorts demonstrate that an increased time to initiate surgical treatment confers lower overall and disease-specific survival for patients with early stage breast cancer. A shortened delay is associated with an outcome benefit comparable in magnitude to the addition of some standard therapies. Although time is required for preoperative evaluation and consideration of options such as reconstruction, efforts to reduce TTT should be pursued where possible to enhance survival.