Objectives: In 2013, the Swiss Medical Board (SMB) concluded that for three breast cancer screens over 13 years in Switzerland, cost-effectiveness was negative, with no additional benefits in quality-adjusted life-years gained. We compared these suggested predicted effects with other estimates. Methods: We used an extensively validated model on the natural history of breast cancer in Switzerland, comparing a 13-year time frame, a life-time perspective, and a continuous screening programme, per 10,000 Swiss women. Both approaches used the Swedish randomized controlled trials for the theoretical effect. Results: Over 13 years, both approaches yield comparable life-years gained (56 versus 67), but in expectation in 10,000 women's lifetimes 444 life-years are gained, and in a continuous screening programme (instead of three screens) 839 years. The SMB estimate of 56 life-years gained is counterweighted by 57 negative quality of life adjusted years, primarily resulting from a 5% annual loss for 10% of women, being false-positive results. International literature is consistent with more than four times lower losses on false-positives. The estimate of overdiagnosed cases in the 13-year time frame was four times higher than in the long-term perspective. Conclusions: By restricting life-years gained to a 13-year time frame the SMB prediction on benefits of mammography screening is unrealistically low. Predicting long-term harms and benefits, specifically tailored to observations, regarding the clinical situation before screening commences, and possible data during a screening programme, are crucial for women, professionals, and policymakers.