Percent Body Weight Lost Calculator

About this calculator

This calculator finds the percentage of body weight lost between a starting weight and a current weight, using the simple formula: (starting weight − current weight) / starting weight × 100. Expressing weight change as a percentage rather than a raw number of kilograms or pounds matters because losing the same 5 kg means something very different to a 100 kg person than to a 60 kg person.

This percentage has a specific clinical meaning: unintentional weight loss of more than about 5% within one month, or more than 10% within six months, is a recognized red flag used in malnutrition screening tools (such as MUST and MST) to identify patients who may need a nutritional assessment or workup for an underlying illness, since significant unplanned weight loss can signal anything from poor appetite to a more serious condition.

Outside the clinical setting, athletes in weight-class sports like wrestling, boxing, and rowing track percent weight lost when cutting weight before competition, and people on structured diets use it to measure progress against their starting point in a way that's comparable across different body sizes.