Expected Weight Loss
Almost every page selling one of these drugs is quoting the same two figures, −14.9% and −20.9%, and both are arm means. A mean is the least informative number a trial produces and the only one that reaches a landing page. Both trials also published where their participants actually landed, and that distribution is what this tool renders.
The arm mean, which is the figure you have already seen
33 lb — 14.9% of 220 lb over 68 weeks, ending near 187 lb. The placebo arm of the same trial averaged 5 lb, and both arms received lifestyle support.
Where 1,961 people actually landed
STEP 1 published the distribution, not only the average. Each row is a threshold the trial reported, the share of this arm that reached it, and the share that did not.
| Threshold | At your weight | Reached it | Did not |
|---|---|---|---|
| 5% or more | 11 lb | 86.4%placebo 31.5% | 13.6% |
| 10% or more | 22 lb | 69.1%placebo 12% | 30.9% |
| 15% or more | 33 lb | 50.5%placebo 4.9% | 49.5% |
STEP 1 reported 5% and 10% and 15% thresholds. The two trials did not publish the same rungs, so the rows differ between molecules. Missing rungs are absent from the papers rather than from this page. Source: STEP 1, PMID 33567185.
Nothing at baseline told anyone which row they would be in
The trial reported the distribution; it did not report a way to place a given person inside it. Starting weight, age and sex did not sort participants into the group that reached a threshold and the group that did not. The rows above describe 1,961 adults with a body-mass index of 30 or higher, or 27 with a weight-related condition, and no diabetes, under 68 weeks of free drug and a full dose escalation, which is not the same arrangement as a monthly subscription. The full STEP 1 record carries the caveats; the cost calculator covers what 68 weeks of it is priced at.
Why an average is the wrong thing to plan around
In STEP 1, 50.5% of the semaglutide arm reached 15% or more. Turned the other way, almost half did not, and 30.9% did not reach 10%. In SURMOUNT-1, 57% of the highest tirzepatide arm reached 20% — so more than two in five people who spent 72 weeks at the top approved dose did not. Neither trial reported anything measured at baseline that separated those groups in advance.
That matters financially as well as clinically, because the decision a reader is making is whether to start paying monthly. A year of this costs four figures at almost every seller on this site, and the trial that produced the headline gave the drug away. What a year actually costs sets that out, and the plateau evidence covers what happens when the curve flattens.
One more gap between the trial and the purchase: both trials ran the approved products at a full, supervised escalation. Most sellers on this site dispense a compounded preparation, which is not FDA-approved and is not reviewed by the FDA for safety, efficacy or quality before dispensing. The figures above describe semaglutide and tirzepatide as studied, not as sold.