Receiving information about expected costs promptly after a cancer diagnosis through psycho‐oncology care or social counselling is crucial for patients to be prepared for the financial impact. Nevertheless, less is known about financial impacts for cancer patients in countries with statutory health insurance. This study aims to explore the full scope of costs that constitute the financial impact of a cancer diagnosis in Germany and to identify the reasons for high financial decline. Semistructured interviews with 39 cancer patients were conducted between May 2017 and April 2018. Narratives were analysed via qualitative content analysis. Several factors influenced cancer patients’ indirect costs and direct medical and non‐medical costs. For many patients, these changes resulted in higher indirect costs caused by income losses, especially when surcharges for shift work, travel expenses or company benefits ceased and were not reimbursed. Higher direct medical costs were caused by co‐payments and additional non‐refundable costs. Non‐medical costs were reported to increase for some patients and to decrease for others, as for example, leisure activity costs either increasing because of pampering oneself to cope with the diagnosis and undergoing therapy or decreasing because of not being able to participate in leisure activities during therapy. When analysing the financial impacts of individuals' total costs, we found that some patients experienced no financial decline or an overall financial increase. Most patients experienced overall higher costs, and income loss was the main driver of a high financial decline. Nevertheless, decreased non‐medical costs due to lower work‐related and leisure activity costs could compensate for these higher costs. Cancer patients are confronted with a variety of changes in their financial situations, even in countries with statutory health insurance. Screening for cancer patients with a high risk of financial decline should consider any effects on indirect costs and direct medical and nonmedical costs.