BE following RT after breast-conserving surgery is a common concern, impacting patients’ quality of life. This study introduces a clinically meaningful classification system for BE and retrospectively evaluates its incidence among patients treated with normofractionated (nfRT) and hypofractionated (hfRT) regimens. Data from 1156 patients treated between 2011 and 2021 were analyzed. BE was graded according to the CTC and a so-called “WST classification” (grade 1: lymphatic drainage performed by the patient; grade 2: professional lymphatic drainage; grade 3: surgery). A total of 33%/17% developed BE according to the WST classification/CTC. Grade III BE was not reported. About 70% experienced a remission of BE during follow-up. Risk factors for the development of BE included RT of lymphatic drainage, complete axillary dissection compared to sentinel node dissection, and CTX. CTX was not confirmed in multivariate analysis. The incidence of BE did not differ significantly between the nfRT and hfRT groups, affirming the safety and comparability of hfRT regarding BE risk (HR: 0.833, p = 0.1219). This study emphasizes the importance of precise and standardized BE classification for improved treatment outcomes. Given its comparable risk profile and potential for enhanced therapy adherence, the findings support hfRT as a preferred regimen aligned with the current guidelines.