GLP-1 Weight Loss Calculator
Quick answer: Trial averages at 12 months: semaglutide ~15% of body weight (STEP-1), tirzepatide ~20% (SURMOUNT-1), retatrutide ~24% in phase 2. Enter your weight to see what those trajectories look like for you — as population averages, not personal predictions.
Projection uses STEP-1 trial averages — population averages with full titration and lifestyle support. Individual results vary widely; roughly 1 in 7 participants were non-responders.
What the projection is based on
Numbers come from the pivotal trials: STEP-1 (semaglutide 2.4 mg, ~15% average loss at 68 weeks), SURMOUNT-1 (tirzepatide 15 mg, ~20%), and Eli Lilly's phase 2 retatrutide data (~24% at 48 weeks, not yet approved). We interpolate the published curves to 3/6/12-month checkpoints. They describe cohorts, not individuals — your response is a coin the trial can't flip for you.
Protecting muscle while losing
A real fraction of rapid GLP-1 weight loss can be lean mass. The evidence-backed countermeasures are unglamorous: protein at 1.8+ g/kg (see the protein calculator), resistance training twice a week minimum, and a deficit that comes from the medication's appetite effect rather than deliberate starvation on top of it.
FAQ
How fast does weight loss start on GLP-1s?+
Trials show meaningful loss from the first month, but the curve is front-flat: early months are titration at low doses, with the steepest loss typically in months 3-9 after reaching therapeutic doses. Slow starts are normal, not failure.
Why might my results differ from the calculator?+
These are trial averages under full titration, dietician support and high adherence. Real-world results scatter widely around them: responders exceed the average, roughly one in seven participants lost little (non-responders), and dose availability or side-effect tolerance changes trajectories.
What happens when you stop taking GLP-1 medication?+
Extension trials (STEP-1 extension, SURMOUNT-4) showed roughly two-thirds of lost weight returning within a year of stopping. Current medical consensus treats these as long-term medications, with habits built during treatment as the buffer.
Educational tool — estimates only, not medical advice. Consult a licensed healthcare provider for individual guidance.