GLP-1 Weight Loss Calculator

GLP-1 weight loss is the weight people lose while taking a medicine that acts like the hormone GLP-1. People lose weight mainly because their appetite drops and they eat less¹. Tirzepatide acts on two hormone receptors, GIP and GLP-1². This calculator takes the average percent change from each medicine's main placebo-controlled trial and applies it to your starting weight.

What the Trial Averages Measure

Each trial reports the average percent change in body weight from the start of treatment to the final week. The averages used here count everyone who was randomized, including people who stopped the medicine early. In STEP 1, that average was 14.9% for semaglutide 2.4 mg, against 16.9% if everyone had taken it as planned¹. The trials enrolled adults with a BMI of 30 or more, or 27 or more with a weight-related health problem, and no diabetes¹ ². Everyone also got diet and activity advice. In STEP 1, that meant a 500-calorie daily deficit and 150 minutes of activity a week¹.

The Formula

Projected weight = Starting weight x (1 + Average % change at week t / 100)

Average % change at week t = Trial average at week T x (1 - e^(-t/23)) / (1 - e^(-T/23))

t = your weeks on treatment. T = the last week of the trial.

The week T averages are copied from the trial papers or US labels. The curve before week T is our estimate, explained below.

How This Calculator Computes Your Result

Enter your starting weight in kg or lb. Choose a medicine and the dose studied in its trial. Then set your weeks on treatment, up to the length of that trial. The tool shows your projected weight, the amount and percent lost, and the placebo group's result at the same week. It also shows the share of each trial group that lost at least 5, 10, 15 and 20 percent, where reported, and the weight each level would mean for you. Weights and percents are rounded to one decimal.

Trial reports give the average only at the final week. For earlier weeks, the tool uses a smooth curve that drops fastest at first and then levels off. Its shape matches two published time points within half a percentage point: 10.6% loss at week 20 on semaglutide in STEP 4, and 20.9% at week 36 on tirzepatide in SURMOUNT-4³ ⁴. For orforglipron, the trial tested 6, 12 and 36 mg of an earlier formulation. The US label lists these results as 5.5, 9 and 17.2 mg tablets⁵. Compounded versions were not tested in these trials.

What Your Result Means

These are the published averages at each trial's final week. If you set the weeks to the end of the trial, your percent change matches these numbers.

Figures come from STEP 1¹, SURMOUNT-1², SCALE as analyzed in the US label⁶ ⁷, OASIS 4⁸ and ATTAIN-1⁹. The placebo column shows what diet and activity advice plus time achieved. The gap between the two columns is the part linked to the medicine. Comparing rows is rough, because the trials differed in length, people and methods.

How Much Results Varied Between People

Averages hide a wide spread. In STEP 1, among people with a week-68 weight, 86.4% of those on semaglutide lost at least 5%, 50.5% lost at least 15%, and 32.0% lost at least 20%¹. That also means about 1 in 7 lost less than 5%. On placebo, 31.5% still lost at least 5%¹. With tirzepatide 15 mg, 91% lost at least 5% and 57% lost at least 20%, compared with 35% and 3% on placebo². With orforglipron 36 mg, 54.6% lost at least 10%, compared with 12.9% on placebo⁹.

When Weight Loss Levels Off

In these trials the dose started low and went up in steps. Semaglutide reached 2.4 mg at week 16¹, and tirzepatide had a 20-week dose increase period². Loss was fastest in the early months and then slowed. In STEP 1, average weight reached its lowest point at about week 60¹. With tirzepatide, slow loss went on well past the first 36 weeks. In SURMOUNT-4, people who kept taking it lost a further 5.5% between weeks 36 and 88⁴.

What Happened When Treatment Stopped

Three trials tested stopping. In the STEP 1 extension, 327 people were followed for a year after their last dose. Those who had taken semaglutide had lost 17.3% and then regained about two-thirds of it, ending 5.6% below their starting weight¹⁰. Most heart and blood sugar markers that had improved drifted back toward where they started¹⁰. In STEP 4, people switched to placebo after 20 weeks of semaglutide regained 6.9% by week 68, while those who continued lost another 7.9%³. In SURMOUNT-4, people switched to placebo after 36 weeks of tirzepatide regained 14.0% by week 88, while those who continued lost another 5.5%⁴. These are group results. Decisions about continuing or stopping belong with your prescriber.