This study reported the prevalence of financial distress (financial toxicity (FT)) and COVID-19-related economic stress in patients with breast cancer (BC). Patients with BC were recruited from the Ciitizen platform, Breastcancer.org, and patient advocacy groups between 30 March and 6 July 2021. FT was assessed with the COmprehensive Score for financial Toxicity (COST) instrument. COVID-19-related economic stress was assessed with the COVID-19 Stress Scale. Among the 669 patients, the mean age was 51.6 years; 9.4% reported a COVID-19 diagnosis. The prevalence rates of mild and moderate/severe FT were 36.8% and 22.4%, respectively. FT was more prevalent in patients with metastatic versus early BC (p < 0.001). The factors associated with FT included income ≤ USD 49,999 (adjusted odds ratio (adj OR) 6.271, p < 0.0001) and USD 50,000–USD 149,999 (adj OR 2.722, p < 0.0001); aged <50 years (adj OR 3.061, p = 0.0012) and 50–64 years (adj OR 3.444, p = 0.0002); living alone (adj OR 1.603, p = 0.0476); and greater depression severity (adj OR 1.155, p < 0.0001). Black patients (adj OR 2.165, p = 0.0133), patients with income ≤ USD 49,999 (adj OR 1.921, p = 0.0432), or greater depression severity (adj OR 1.090, p < 0.0001) were more likely to experience COVID-19-related economic stress. FT was common in patients with BC, particularly metastatic disease, during COVID-19. Multiple factors, especially lower income and greater depression severity were associated with financial difficulties during COVID-19.