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Objectives To estimate overdiagnosis in Denmark for all invasive cancers, with a focus on prostate, breast, renal, thyroid cancers, and melanoma.Method In this nationwide population-based registry study of all Danish citizens from 1982 to 2018, we estimated the proportion of overdiagnosed cancers in 2018, including prostate, breast, renal, thyroid cancers, melanoma, and other invasive cancers. To estimate overdiagnosis, we compared the lifetime cancer risks in 1982 and 2018, using age-specific incidence rates from both years and age-specific mortality rates from 2018 for both calculations.Results Estimated for women/men in 2018, 33%/-16% of breast cancers, 60%/59% of thyroid cancers, 77%/80% of melanomas, 11%/32% of renal cancers, -/50% of prostate cancer, and 6%/-4% of other invasive cancers were overdiagnosed, or 15%/17% of all invasive cancer diagnosesConclusions We observed substantial overdiagnosis in Denmark, particularly for the five cancer types under study. Given that these estimates encompass major cancers for which systematic screening or early detection initiatives have been implemented, they indicate a significant waste of resources and point to a clear solution: these initiatives should be scaled back.