This article presents a tool to calculate health care costs attributable to overweight in a comparable and standardized way. The purpose is to describe the method-ological principles of the tool and to put it into use by calculating and comparing the costs attributable to over-weight for The Netherlands, Germany and Czech Republic. The tool uses a top-down and prevalence-based approach, consisting of five steps. Step one identifies overweight-related diseases and age-and gender-specific relative risks. Included diseases are ischemic heart disease, stroke, hypertension, type 2 diabetes mellitus, colorectal cancer, postmenopausal breast cancer, endometrial cancer, kidney cancer and osteoarthritis. Step two consists of collecting data on the age-and gender-specific prevalence of these diseases. Step three uses the population-attributable prev-alence to determine the part of the prevalence of these diseases that is attributable to overweight. Step four cal-culates the health care costs associated with these diseases. Step five calculates the costs of these diseases that are attributable to overweight. Overweight is responsible for 20–26 % of the direct costs of included diseases, with sensitivity analyses varying this percentage between 15–31 %. Percentage of costs attributable to obesity and preobesity is about the same. Diseases with the highest percentage of costs due to overweight are diabetes, endo-metrial cancer and osteoarthritis. Disease costs attributable to overweight as a percentage of total health care expen-ditures range from 2 to 4 %. Data are consistent for all three countries, resulting in roughly a quarter of costs of included diseases being attributable to overweight.