GLP-1 Weight Loss Calculator (Semaglutide & Tirzepatide Expected Results)

How it works

expected loss (%) at week t ≈ L × (1 − e^(−t/20)) ÷ (1 − e^(−T/20)), held at L after week T · L, T = trial mean loss and duration: semaglutide 2.4 mg 14.9% at 68 weeks (STEP 1); tirzepatide 5 / 10 / 15 mg 15.0% / 19.5% / 20.9% at 72 weeks (SURMOUNT-1); placebo 2.4% and 3.1% · expected weight = start × (1 − loss%)

GLP-1–based medicines produce weight loss that is fast in the first months and levels off after about a year. In the STEP 1 trial, adults without diabetes taking semaglutide 2.4 mg weekly lost on average 14.9% of their body weight over 68 weeks; in SURMOUNT-1, tirzepatide lost 15.0%, 19.5% and 20.9% at 5, 10 and 15 mg over 72 weeks — all alongside diet and exercise advice. This calculator fits a smooth curve through those averages (including the dose-escalation months) to estimate where you might be after a given number of weeks. People with type 2 diabetes typically lose less.

Worked example

Starting at 100 kg on semaglutide 2.4 mg, after 52 weeks the trial-average curve gives a loss of about 14.3%, so the expected weight is 85.7 kg (14.3 kg lost). With lifestyle changes alone (the trial placebo group) the loss would be about 2.3 kg.

Sources: Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). NEJM 2021 · Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). NEJM 2022

Frequently asked questions