Background: National guidelines endorse time-dependent quality metrics for breast cancer care. We examined factors associated with delays in chemotherapy initiation at an NCI-Designated Comprehensive Cancer Center. Patients and Methods: We identified 523 patients who received postoperative adjuvant chemotherapy between January 2011 and December 2013 at our center. We defined 28 days from last definitive surgery (LDS) to chemotherapy as the target time frame, and an unacceptable delay in chemotherapy initiation (UCD) as greater than 42 days from LDS. Multivariate regression models were used to identify factors associated with UCD and the impact of Oncotype DX testing in patients with hormone receptor (HR)–positive breast cancer. Results: Median days between LDS and chemotherapy initiation was 34 (interquartile range, 15), with 30% of patients starting within 28 days of LDS and 26.9% having UCD. Tumor characteristics such as subtype and stage affected UCD; patients with HR-positive or HER2-positive tumors were more likely to be delayed compared with those with triple-negative breast cancer. Patients with stage I disease, those undergoing mastectomy with or without immediate reconstruction, and those whose pathology sign-out was greater than 10 days postoperatively were more likely to be delayed. A higher proportion of UCD was found in HR-positive patients (31%) for whom Oncotype DX testing was ordered compared with those in whom it was not ordered (20%). Conclusions: This study provides insight into subpopulations that may be at risk to experience delays in chemotherapy initiation, directing interventions to improve the timeliness of care.