GLP-1 weight-regain calculator

How this is calculated (and the research behind it)

The anchor is trial-measured. In the STEP 1 trial extension, people who stopped semaglutide regained about two-thirds of their lost weight within twelve months: mean net weight loss fell from 17.3 percent to 5.6 percent.¹ That two-thirds figure is the red line, and it is what the best available trial shows for a full stop. Most people face this transition, since roughly 65 percent discontinue within a year.²

The taper and muscle lines are modeled, not measured. No trial isolates a taper schedule or a muscle-preservation protocol against regain, so the calculator projects a gradual taper and preserved muscle as reducing regain relative to a cold stop. That direction is well supported in principle, a slower return of appetite, continued treatment, and more metabolically active muscle all blunt rebound, but the exact size of the effect is an estimate. Treat the green line as a direction you can influence, not a promise.

Why muscle changes the picture. Reviews of GLP-1 body-composition data place lean mass at roughly 15 to 40 percent of total weight lost,³ and resistance training has been shown to offset most diet-induced lean loss.⁵ The regain risk is not only how many pounds return but their composition: regaining fat while muscle stays low trends toward sarcopenic obesity.⁴ Arriving at your exit with muscle intact is the variable you most control.

The four phases, and where muscle decides the ending

The diagram above traces the journey in four phases. During active loss the medication suppresses appetite and weight falls fast, and this is when composition is set, because without countermeasures roughly 15 to 40 percent of what you lose can be lean mass.³ The plateau is where weight settles. The off-ramp, whether a cold stop or a gradual taper, is where appetite returns: in the STEP 1 trial extension people regained about two-thirds of their lost weight within a year of stopping semaglutide, and since roughly 65 percent of users discontinue within twelve months, most people reach this phase.¹² Maintenance is the ending, and it splits in two. If you preserved muscle on the way down, you arrive with more metabolically active tissue and more reserve. If you did not, weight can return as fat while muscle stays low, the pattern that trends toward sarcopenic obesity.⁴ The muscle you build during the loss phase is the reserve you spend later.

Honest limits

The two-thirds figure comes from one population (semaglutide, STEP 1) and your result may differ. The taper and muscle adjustments are illustrative projections, not trial outcomes, and the curve shape assumes regain is front-loaded and then plateaus. This is a planning tool to show the shape of the risk and the levers you hold, not a prediction of your body. Decisions about staying on, tapering, or stopping a GLP-1 belong to you and your prescriber.