A percentage describes a change relative to a starting value. It helps put a weight change into context, but does not predict your response to a medicine, diet or exercise program.
Calculate a change in weight
Your entries stay in this browser. They are not submitted or saved. This calculation is information, not a diagnosis or a treatment recommendation.
The formula
Weight lost = starting weight − current weight.
Percentage weight loss = (starting weight − current weight) ÷ starting weight × 100.
Use kilograms for both values, or pounds for both. The percentage is the same regardless of which unit you choose. A current weight above the starting weight represents weight gain rather than loss.
A worked example
An illustrative change from 200 lb to 180 lb is 20 lb, or 10% of the starting weight: (200 − 180) ÷ 200 × 100. This example is arithmetic, not a recommended target.
What would 5%, 10%, 15%, 20% or 25% mean?
Multiply starting weight by the selected percentage divided by 100 to find the absolute change. Subtract that change from starting weight to find the remaining weight. The calculator shows these scenarios after a valid calculation. They are not a promise of benefit or suggested treatment goals.
Using percentages from a clinical trial
A published average depends on the study population, intervention, duration, missing-data method and analysis. A percentage from one trial should not be treated as a head-to-head comparison with another trial. The Clinical Trial Tracker keeps those distinctions alongside sources.
Daily body-weight changes can include water and food, and a scale does not separate fat from muscle. Read our sustainable weight-management guide for broader context.
Privacy and limitations
No measurement is sent, saved or added to analytics by this calculator. It cannot diagnose a condition, choose a medicine or recommend a dose. Discuss treatment goals with a qualified professional who knows your circumstances. Medical disclaimer.