How Our GLP-1 Weight-Loss Calculator Works

Last updated October 13, 2026

Short answer: the calculator takes your current weight and goal weight, then projects a month-by-month timeline using an approach-to-plateau curve calibrated to the average outcomes reported in the STEP 1 (semaglutide) and SURMOUNT-1 (tirzepatide) clinical trials.

What goes into the estimate

• Your current weight
• Your goal weight
• A plateau percentage for each medication (~14.9% for semaglutide, ~20.9% for tirzepatide), drawn from published trial averages
• An approach-to-plateau rate reflecting how quickly each medication's trial population trended toward that plateau

The exact model and source data

For anyone who wants to check or cite the numbers directly, this is the full model, not a simplification of it:

The projected weight at month t is:

weight(t) = currentWeight − (currentWeight × plateau%) × (1 − e^(−t / tau))

The result is capped at your goal weight, it never projects you losing more than you asked to lose. A lower tau means faster early progress toward the plateau, tirzepatide's trial population showed a steeper early trajectory than semaglutide's at comparable timepoints, which is why its tau is lower. The chart shows the first 24 months. The curve approaches its plateau but never crosses it, so the month your goal is reached has an exact answer only when your goal is inside the plateau. In that case we report the month, and flag it when it runs longer than the roughly 17 months the trials covered. If your goal is beyond the plateau, the model never reaches it, so we do not invent a month count. We show where the projection levels off instead.

What doesn't change the estimate

We ask for age and sex during the calculator flow for context, but the weight-loss projection itself is driven by your starting weight, goal weight, and the medication's trial-average curve. The calculator doesn't account for dosage titration, diet, exercise, or individual metabolic differences, all of which can meaningfully affect a real person's results.

Why it's an estimate, not a prediction

Clinical trials report averages across hundreds of participants. Any individual can reasonably land above or below that average. The calculator is meant to set realistic expectations for the shape and pace of a GLP-1 weight-loss timeline, not to forecast your exact outcome. A licensed provider is the only reliable source for a personalized medical assessment.