GLP-1 Weight Loss Projection Calculator
Estimated Results Based on STEP, SURMOUNT & SCALE Clinical Trials
How GLP-1 Receptor Agonists Work
GLP-1 (glucagon-like peptide-1) receptor agonists are a class of medications originally developed for type 2 diabetes that have shown remarkable efficacy for weight management. They work through multiple complementary mechanisms:
Appetite Regulation
GLP-1 receptor agonists act on receptors in the hypothalamus — the brain region that controls hunger and satiety. They increase feelings of fullness (satiety) and reduce appetite, leading to a natural decrease in caloric intake. Most patients report feeling satisfied with smaller portions and experiencing fewer food cravings.
Gastric Emptying
These medications slow the rate at which food leaves the stomach (delayed gastric emptying). This means food stays in the stomach longer, prolonging feelings of fullness after meals and reducing the urge to eat again soon after.
Insulin and Blood Sugar Regulation
GLP-1 agonists enhance glucose-dependent insulin secretion, meaning they help the pancreas release insulin more effectively when blood sugar is elevated. They also suppress glucagon (a hormone that raises blood sugar), which helps stabilize blood glucose levels throughout the day.
Tirzepatide: Dual Action
Tirzepatide (Mounjaro/Zepbound) is unique because it activates both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. This dual mechanism appears to produce greater weight loss than GLP-1 agonists alone, as GIP receptors also play a role in fat metabolism and energy balance.
How They Are Administered
All three medications covered here are administered as subcutaneous injections. Semaglutide and tirzepatide are given once weekly, while liraglutide is given once daily. Doses are gradually increased over several weeks to minimize gastrointestinal side effects.
Clinical Trial Results Summary
STEP 1 — Semaglutide 2.4mg (Wegovy)
The STEP 1 trial (Wilding et al., 2021) enrolled 1,961 adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity. Key findings:
- Mean body weight reduction of 14.9% at 68 weeks vs. 2.4% with placebo
- 86.4% of participants achieved ≥5% weight loss
- 69.1% achieved ≥10% weight loss
- 50.5% achieved ≥15% weight loss
- Significant improvements in cardiometabolic risk factors including waist circumference, blood pressure, and lipid levels
SURMOUNT-1 — Tirzepatide 15mg (Zepbound)
The SURMOUNT-1 trial (Jastreboff et al., 2022) enrolled 2,539 adults with obesity or overweight. At the highest dose (15mg), results showed:
- Mean body weight reduction of 20.9% at 72 weeks vs. 3.1% with placebo
- 96% of participants achieved ≥5% weight loss
- 89.5% achieved ≥10% weight loss
- 78.1% achieved ≥15% weight loss
- 56.7% achieved ≥20% weight loss
- Currently the most effective GLP-1 medication for weight loss based on clinical trial data
SCALE — Liraglutide 3.0mg (Saxenda)
The SCALE Obesity and Prediabetes trial (Pi-Sunyer et al., 2015) enrolled 3,731 adults. Key findings:
- Mean body weight reduction of 8.0% at 56 weeks vs. 2.6% with placebo
- 63.2% of participants achieved ≥5% weight loss
- 33.1% achieved ≥10% weight loss
- Liraglutide was the first GLP-1 agonist approved specifically for weight management (2014)
- Requires daily injection (vs. weekly for semaglutide and tirzepatide)
Important Context
All trials included lifestyle intervention (reduced-calorie diet and increased physical activity) for both the treatment and placebo groups. Results represent mean values — individual outcomes varied widely. Participants with higher starting BMI tended to lose more absolute weight but similar percentages.
Side Effects and Safety Considerations
Common Side Effects (Gastrointestinal)
The most frequently reported side effects are gastrointestinal and tend to occur during dose escalation:
- Nausea (20–44% of patients) — typically mild to moderate and improves over time
- Diarrhea (15–30%) — usually transient
- Vomiting (6–24%) — more common during dose increases
- Constipation (10–24%) — due to slowed gastric emptying
- Abdominal pain (6–20%)
- Decreased appetite — this is part of the therapeutic mechanism
Serious but Rare Side Effects
- Pancreatitis: Inflammation of the pancreas has been reported. Seek immediate medical attention for severe abdominal pain that radiates to the back.
- Thyroid C-cell tumors: In animal studies, GLP-1 agonists caused thyroid C-cell tumors in rodents. Relevance to humans is uncertain, but these medications carry a boxed warning and are contraindicated in patients with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
- Gallbladder problems: Rapid weight loss can increase the risk of gallstones (cholelithiasis).
- Hypoglycemia: Low blood sugar risk is higher when combined with insulin or sulfonylureas.
- Kidney injury: Dehydration from gastrointestinal side effects can affect kidney function in rare cases.
Managing Side Effects
- Eat smaller, more frequent meals
- Avoid high-fat and greasy foods, especially during dose escalation
- Stay well hydrated
- Eat slowly and stop when you feel full
- Follow the gradual dose escalation schedule — do not increase doses faster than prescribed
- Report persistent or severe symptoms to your healthcare provider
Optimizing Results with Lifestyle Changes
GLP-1 medications are most effective when combined with lifestyle modifications. Clinical trials required all participants to follow a reduced-calorie diet and increase physical activity. Here is how to maximize your results:
Protein Intake
Adequate protein is critical during GLP-1-mediated weight loss to preserve lean muscle mass. Recommendations include:
- Aim for 1.0–1.2 g of protein per kg of body weight per day (or ~0.5 g per lb)
- Since appetite is reduced, prioritize protein at every meal
- Good sources: lean meats, fish, eggs, Greek yogurt, legumes, tofu
- Consider a protein supplement if struggling to meet targets with reduced food intake
Exercise
Resistance training is particularly important to preserve muscle mass during weight loss:
- Resistance training: 2–3 sessions per week targeting major muscle groups
- Aerobic exercise: 150–300 minutes per week of moderate-intensity activity (brisk walking, cycling, swimming)
- Start gradually and increase intensity over time
- Exercise helps maintain muscle mass, improve insulin sensitivity, and support long-term weight maintenance
Hydration
- Drink at least 64 oz (2 liters) of water daily
- Increase fluid intake if experiencing gastrointestinal side effects (nausea, vomiting, diarrhea)
- Dehydration can increase the risk of constipation, kidney problems, and dizziness
- Limit sugary beverages and alcohol
Dietary Quality
- Focus on nutrient-dense foods since overall intake will be reduced
- Emphasize vegetables, fruits, whole grains, lean proteins, and healthy fats
- Limit ultra-processed foods, added sugars, and refined carbohydrates
- A calorie deficit of 500–750 calories per day is typically recommended alongside medication
Monitoring and Follow-Up
- Regular check-ins with your healthcare provider (typically every 4–12 weeks)
- Monitor weight, blood pressure, blood sugar, and lipid levels
- Track your food intake, especially protein, during the initial months
- Discuss any side effects promptly so your provider can adjust your plan
Frequently Asked Questions
This calculator uses mean (average) weight loss data from major published clinical trials: STEP 1 for semaglutide, SURMOUNT-1 for tirzepatide, and SCALE for liraglutide. These are population-level averages — in the trials, some participants lost significantly more weight than the average, while others lost less. Your individual results will depend on many factors including your starting weight, adherence to the medication, diet quality, exercise habits, genetics, metabolic factors, and any concurrent medical conditions. The calculator provides a reasonable estimate of what clinical trial participants experienced on average, but it should not be interpreted as a guarantee of personal outcomes.
Based on currently published clinical trial data, tirzepatide (Mounjaro/Zepbound) at the 15mg dose has shown the greatest average weight loss at approximately 20.9% of body weight at 72 weeks in the SURMOUNT-1 trial. Semaglutide (Wegovy) at 2.4mg showed approximately 14.9% weight loss at 68 weeks in STEP 1, and liraglutide (Saxenda) at 3.0mg showed approximately 8.0% at 56 weeks in SCALE. However, “most effective” may differ for each individual — factors like side effect tolerance, injection frequency preference (daily vs. weekly), cost, insurance coverage, and individual metabolic response all play a role. Your healthcare provider can help determine which medication is best suited for your situation.
Most patients begin to notice weight loss within the first 4–8 weeks of treatment, though the initial weeks often involve dose titration (gradually increasing the dose) to minimize side effects. Meaningful weight loss (5% or more of body weight) is typically achieved by 12–16 weeks on therapeutic doses. The rate of weight loss is generally fastest during the first 20–30 weeks and then plateaus as the body reaches a new metabolic equilibrium. In the STEP 1 trial, most weight loss with semaglutide occurred between weeks 8 and 52, with minimal additional loss between weeks 52 and 68. Patience and consistency are important — the full benefit of these medications develops over many months.
Research consistently shows that weight regain occurs after discontinuing GLP-1 medications. The STEP 1 extension trial (Wilding et al., 2022) found that participants who stopped semaglutide regained approximately two-thirds of their lost weight within one year of discontinuation. Similarly, improvements in cardiometabolic risk factors (blood pressure, blood sugar, lipids) also partially reversed. This is because obesity is a chronic condition — the medications manage it but do not cure it, similar to how blood pressure medications manage hypertension. Many healthcare providers now recommend long-term or indefinite use for sustained benefits. If discontinuation is planned, a gradual taper combined with intensified lifestyle modifications may help slow the rate of weight regain.
GLP-1 receptor agonists have been used for type 2 diabetes management for over 15 years, and their safety profile is well-established in that context. For weight management specifically, long-term data continues to accumulate. The SELECT trial (2023) demonstrated that semaglutide 2.4mg reduced major cardiovascular events by 20% in overweight and obese adults over a median of 3.3 years, suggesting cardiovascular benefits beyond weight loss alone. Common gastrointestinal side effects (nausea, vomiting, diarrhea) typically improve within the first few months. Rare but serious risks include pancreatitis, gallbladder disease, and a theoretical risk of thyroid C-cell tumors (seen in rodent studies). Ongoing monitoring by your healthcare provider is essential. The benefits of sustained weight loss (reduced risk of type 2 diabetes, cardiovascular disease, sleep apnea, and certain cancers) generally outweigh the risks for most eligible patients.
GLP-1 receptor agonists are contraindicated in several populations: (1) Individuals with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2); (2) Those with a history of severe hypersensitivity to the specific medication or its components; (3) Pregnant or breastfeeding women — these medications should be discontinued at least 2 months before a planned pregnancy; (4) Individuals with a history of pancreatitis should use these medications with caution. Additionally, they are generally not recommended for individuals with type 1 diabetes, severe gastrointestinal disease (such as gastroparesis), or end-stage renal disease. GLP-1 medications are typically prescribed for adults with a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related comorbidity. Always consult your healthcare provider to determine if these medications are appropriate for your specific health situation.
Medical Disclaimer
This GLP-1 Weight Loss Projection Calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Projections are based on published clinical trial averages and may not reflect your individual results. Weight loss outcomes depend on many factors including diet, exercise, genetics, adherence, and individual metabolic response. GLP-1 medications require a prescription and should only be used under the supervision of a qualified healthcare provider. Do not start, stop, or change any medication regimen without consulting your healthcare provider. All calculations are performed in your browser — no personal data is stored on our servers or shared with any third party.
References
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216. doi:10.1056/NEJMoa2206038
- Pi-Sunyer X, Astrup A, Fujioka K, et al. A randomized, controlled trial of 3.0 mg of liraglutide in weight management. N Engl J Med. 2015;373(1):11–22. doi:10.1056/NEJMoa1411892
- Garvey WT, Batterham RL, Bhatta M, et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nat Med. 2022;28(10):2083–2091. doi:10.1038/s41591-022-02026-4
- Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553–1564. doi:10.1111/dom.14725
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221–2232. doi:10.1056/NEJMoa2307563
Clinical Data Sources: STEP 1 (Wilding et al., 2021), SURMOUNT-1 (Jastreboff et al., 2022), SCALE (Pi-Sunyer et al., 2015). Projections reflect mean weight loss reported in published peer-reviewed trials.