What the trials found
In STEP 1, adults with obesity or overweight taking semaglutide 2.4 mg weekly, with lifestyle support, lost an average of 14.9% of body weight over 68 weeks, compared with 2.4% on placebo.
In SURMOUNT-1, tirzepatide produced average losses of 15.0% (5 mg), 19.5% (10 mg) and 20.9% (15 mg) over 72 weeks, compared with 3.1% on placebo.
| Medication and dose | Trial | Length | Average loss | Placebo |
|---|---|---|---|---|
| Semaglutide 2.4 mg (Wegovy) | STEP 1 | 68 weeks | 14.9% | 2.4% |
| Tirzepatide 5 mg | SURMOUNT-1 | 72 weeks | 15.0% | 3.1% |
| Tirzepatide 10 mg | SURMOUNT-1 | 72 weeks | 19.5% | 3.1% |
| Tirzepatide 15 mg | SURMOUNT-1 | 72 weeks | 20.9% | 3.1% |
How the month-by-month curve is drawn
Trial participants lose weight slowly at first while the dose is increased every four weeks, fastest between roughly months 2 and 8, then more slowly until a plateau around week 60.
The calculator draws a smooth curve with that shape and scales it so it ends exactly at the trial's average. It is an illustration of the average path, not a forecast of yours.
Example: starting at 104 kg (230 lb) on semaglutide 2.4 mg, the trial average of 14.9% works out to about 15.5 kg (34 lb) over 68 weeks.
Why your results may differ
Individual results in both trials varied widely. Starting weight, dose reached, side effects, diet, activity, sleep, other medications and conditions like type 2 diabetes all change the outcome. People with type 2 diabetes tend to lose less.
Trial participants also received lifestyle counseling and regular follow-up. Real-world results are often somewhat lower than trial averages.
Protect your muscle on a GLP-1
A meaningful share of weight lost on GLP-1 medications can be lean mass, not fat. Eating enough protein and doing strength training two to three times a week are the two best-supported ways to keep more muscle.
Track more than the scale: waist, body measurements and progress photos show whether you are losing fat or muscle, and the scale alone cannot.
Safety
GLP-1 medications are prescription drugs. Dosing, dose increases and whether a medication is right for you are decisions for you and your prescriber. Do not use compounded or online products outside of medical supervision. This calculator gives no dosing advice.
GLP-1 weight loss chart by month
This chart shows the calculator's average curve for someone starting at 100 kg (220 lb). Because the start is 100 kg, the kilos lost equal the percentage lost. For any other starting weight, multiply your weight by the percentage.
The last row is the end of each trial: 68 weeks for semaglutide and 72 weeks for tirzepatide. These are trial averages, not a prediction for you.
| Month | Semaglutide 2.4 mg (Wegovy) | Tirzepatide 10 mg (Zepbound, Mounjaro) | Tirzepatide 15 mg (Zepbound, Mounjaro) |
|---|---|---|---|
| 1 | 97.8 kg (-2.2%) | 97.1 kg (-2.9%) | 96.9 kg (-3.1%) |
| 2 | 95.4 kg (-4.6%) | 94.0 kg (-6.0%) | 93.5 kg (-6.5%) |
| 3 | 93.2 kg (-6.8%) | 91.2 kg (-8.8%) | 90.5 kg (-9.5%) |
| 6 | 88.7 kg (-11.3%) | 85.3 kg (-14.7%) | 84.3 kg (-15.7%) |
| 9 | 86.5 kg (-13.5%) | 82.4 kg (-17.6%) | 81.2 kg (-18.8%) |
| 12 | 85.6 kg (-14.4%) | 81.2 kg (-18.8%) | 79.8 kg (-20.2%) |
| End of trial | 85.1 kg (-14.9%) | 80.5 kg (-19.5%) | 79.1 kg (-20.9%) |