Abstract Background The purpose of the study was to quantify the association between body weight and health by estimating the expected lifetime with and without diabetes (diabetes-free life expectancy) at age 30 and 65. In addition, the diabetes-free life expectancy was stratified by educational level. Methods Life tables by sex, level of education and obese/not obese were constructed using nationwide register data and self-reported data on body weight and height and diabetes from the Danish National Health Survey in 2021. Diabetes-free life expectancies were estimated by Sullivan’s method. Results The difference in life expectancy between not obese 30-year-old men with a long and a short education was 5.7 years. For not obese women, the difference was 4.1 years. For obese men and women, the difference in life expectancy at age 30 was 7.0 and 5.2 years. Women could expect more years without and fewer years with diabetes than men regardless of body weight and educational level. Diabetes-free life expectancy differed by 6.9 years between not obese 30-year-old men with a short and a long education and by 7.7 years for obese men with a short and a long education. For women, the differences were 5.9 and 6.6 years. Conclusion The results demonstrate an association of obesity and educational level with life expectancy and diabetes-free life expectancy. There is a need for preventive efforts to reduce educational inequality in life expectancy and diabetes-free life expectancy. Structural intervention will particularly benefit overweight people with short education.