PeptideWise

GLP-1 Weight Loss Calculator

GLP-1 receptor agonists — including semaglutide (sold as Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound) — represent a significant advance in obesity pharmacotherapy. Large randomized controlled trials have demonstrated average weight reductions of 15–21% of body weight when used at maintenance doses with lifestyle modification.

This calculator projects an individualized weight loss timeline based on STEP and SURMOUNT clinical trial averages. Enter your starting weight, height, and medication to generate a month-by-month projection along with the standard dose escalation schedule.

Starting weight
Height (for BMI calculation)
Sex
Medication

Enter your weight above to see your projected timeline.

Semaglutide Dose Escalation Schedule

PeriodDose
Weeks 1–40.25 mg
Weeks 5–80.5 mg
Weeks 9–121.0 mg
Weeks 13–161.7 mg
Weeks 17+2.4 mg (maintenance)

About GLP-1 Receptor Agonists

GLP-1 (glucagon-like peptide-1) is an incretin hormone secreted by L-cells in the intestinal epithelium in response to nutrient intake. It stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite via central nervous system receptors in the hypothalamus and brainstem.

Semaglutide is a GLP-1 receptor agonist with 94% amino acid sequence homology to native human GLP-1. Tirzepatide is a dual GIP/GLP-1 receptor agonist — it activates both the GLP-1 receptor and the GIP (glucose-dependent insulinotropic polypeptide) receptor, which may synergistically enhance weight loss efficacy.

The STEP 1 trial (n=1961) demonstrated a mean weight reduction of 14.9% with semaglutide 2.4 mg weekly over 68 weeks. The SURMOUNT-1 trial (n=2539) demonstrated a mean weight reduction of 20.9% with tirzepatide 15 mg weekly over 72 weeks. Both trials required lifestyle intervention in addition to pharmacotherapy.

How to Interpret These Projections

The monthly weight loss rates in this calculator are derived from the average efficacy curves reported in pivotal clinical trials. Early months typically show faster loss as appetite suppression takes effect; later months reflect the natural plateau as the body adapts. The projections cap at the trial-average total loss percentages — some individuals lose more, many lose less.

Limitations

  • Projections are based on average clinical trial results from STEP 1 (semaglutide) and SURMOUNT-1 (tirzepatide). Individual results vary significantly based on diet, exercise, adherence, and metabolic factors.
  • This calculator assumes full dose escalation to maintenance dose. Many patients cannot tolerate the maximum dose or require modified escalation.
  • The timeline model is a simplified approximation. Actual weight loss is nonlinear and highly individual.
  • BMI is a limited metric and does not account for body composition, muscle mass, or ethnicity-specific health thresholds.
  • This tool does not account for drug interactions, contraindications, or individual medical history.
  • Cost estimates are approximate retail prices and vary by pharmacy, insurance coverage, and manufacturer coupon availability.
  • This tool is for educational and research reference purposes only. It does not constitute medical advice.

Sources and References

  1. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1 Trial). New England Journal of Medicine, 2021.
  2. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1 Trial). New England Journal of Medicine, 2022.
  3. Wegovy (semaglutide) Prescribing Information. Novo Nordisk / U.S. Food and Drug Administration.
  4. Zepbound (tirzepatide) Prescribing Information. Eli Lilly / U.S. Food and Drug Administration.

Frequently Asked Questions

How does a GLP-1 receptor agonist cause weight loss?
GLP-1 (glucagon-like peptide-1) receptor agonists mimic a naturally occurring gut hormone that is released after eating. They reduce appetite by acting on hypothalamic receptors, slow gastric emptying so you feel full longer, and decrease food cravings. Semaglutide and tirzepatide both activate GLP-1 receptors; tirzepatide additionally activates GIP (glucose-dependent insulinotropic polypeptide) receptors, which may explain its greater average weight loss in trials.
What do clinical trials show about average weight loss?
The STEP 1 trial (semaglutide 2.4 mg) showed an average body weight reduction of approximately 14.9% over 68 weeks. The SURMOUNT-1 trial (tirzepatide 15 mg) showed an average reduction of approximately 20.9% over 72 weeks. These figures are averages across trial participants — individual results varied substantially.
Why does weight loss plateau after several months?
The body adapts to weight loss through several compensatory mechanisms: reduced resting metabolic rate, hormonal changes that increase hunger (rising ghrelin, falling leptin), and increased caloric efficiency. This is sometimes called metabolic adaptation. GLP-1 agonists suppress appetite but cannot fully override these physiological adaptations at higher dose levels.
How can I preserve muscle mass during GLP-1 therapy?
Research suggests that resistance training (weight lifting) 2-3 times per week, combined with adequate protein intake (1.2-1.6 g per kg of body weight per day), helps preserve lean muscle mass during rapid weight loss on GLP-1 therapy. Studies on semaglutide show that roughly 25-40% of weight lost can be lean mass without exercise intervention, making resistance training important.
Who is eligible for GLP-1 therapy for weight loss?
FDA-approved indications for semaglutide (Wegovy) and tirzepatide (Zepbound) for chronic weight management include adults with a BMI of 30 or higher, or a BMI of 27 or higher with at least one weight-related comorbidity (such as type 2 diabetes, hypertension, or dyslipidemia). Eligibility is determined by a licensed healthcare provider.
What are the most common side effects?
The most common side effects are gastrointestinal: nausea, vomiting, diarrhea, and constipation. These are most pronounced when starting the medication and during dose escalation, and typically improve over time. The slow dose escalation schedule is specifically designed to minimize these effects. More serious but rare risks include pancreatitis, gallbladder disease, and thyroid C-cell tumors (in animal studies). Discuss the full risk profile with a healthcare provider.
What happens if I stop taking the medication?
Clinical trial data shows that most patients regain significant weight after stopping GLP-1 therapy. The STEP 4 trial found participants regained two-thirds of their lost weight within one year of stopping semaglutide. This suggests GLP-1 agonists require long-term use to maintain weight loss, similar to other chronic disease medications.