GLP-1 weight-loss projector: what the trials averaged

“How much will I lose?” is the first question everyone asks, and the honest answer is a range, not a number. This tool takes the results from the pivotal trials — STEP for semaglutide, SURMOUNT for tirzepatide — and applies the average, and the spread around it, to your weight. It will not flatter you with a single confident figure, because the trials do not support one.

These are trial averages, not a prediction for you. Real results vary widely — some people lose much more, some much less, and some do not respond. The numbers assume the full dose, reached over months, alongside diet and exercise support — and weight usually returns if the drug is stopped.

1. Your current weightlb

2. Which medication?

Wegovy (semaglutide 2.4 mg)Zepbound (tirzepatide, top dose)

Enter your weight to see the projection. You will get the trial average applied to you, plus the honest range most people fall in. Nothing is stored or sent anywhere.

This projector applies published trial averages to your weight for illustration. It is not a prediction, a medical assessment, or a promise of results, and it cannot account for your health, dose, or how you respond. Everything computes in your browser and nothing is stored or sent anywhere.

Where the numbers come from

In STEP 1, adults with obesity but without diabetes taking semaglutide 2.4 mg (Wegovy) lost about 15% of their body weight on average by 68 weeks, versus about 2.4% on placebo — with lifestyle counselling in both groups. In SURMOUNT-1, tirzepatide (Zepbound) averaged about 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg by 72 weeks. Those are the figures this tool uses. They are means: individuals scattered widely on either side.

Why a range is the honest answer

Averages hide the spread, and the spread here is large. In STEP 1, roughly a third of people lost 20% or more, while others lost relatively little. Response depends on biology, dose reached, side-effect tolerance, and the lifestyle changes alongside — which is why a projector that hands you one number is quietly overpromising. The band this tool shows is where many people land, not a boundary.

Three things the projection can't show

It takes time. These results are at roughly 15–18 months, after slowly titrating to the full dose — see how the dose steps up. Some of the loss is muscle, which matters more for midlife women already losing muscle and bone — see muscle loss and bone density. And weight tends to return if you stop: withdrawal studies found most of the loss came back within about a year, because obesity is a chronic condition, not a course you finish — see weight regain after stopping.

Before you fixate on a number

Check whether you meet the label criteria with the GLP-1 eligibility checker, whether your plan is likely to pay with the Cost & Coverage Estimator, and — if midlife weight is your reason — read GLP-1s for menopause weight gain. Weight loss is one measure of success; how you feel, move, and protect your muscle and bone are others.