The GLP-1 Weight Loss Timeline Calculator projects the expected trajectory of weight loss for patients taking glucagon-like peptide-1 (GLP-1) receptor agonist medications, specifically semaglutide (marketed as Ozempic and Wegovy) and tirzepatide (marketed as Mounjaro and Zepbound). These medications have transformed the treatment of obesity and type 2 diabetes since their approval, producing average total body weight losses of 15 to 22 percent over 68 to 72 weeks in pivotal clinical trials. The calculator uses published dose-escalation schedules and weight-loss curves from the STEP and SURMOUNT trial programs to model expected results at each treatment milestone. GLP-1 receptor agonists work by mimicking the incretin hormone GLP-1, which is naturally released from the gut after eating. The medication slows gastric emptying, reduces appetite through hypothalamic signaling, and improves insulin sensitivity. Tirzepatide additionally activates the glucose-dependent insulinotropic polypeptide (GIP) receptor, providing a dual-agonist mechanism that produces somewhat greater weight loss than semaglutide alone. Both medications are administered as once-weekly subcutaneous injections and require gradual dose escalation over 16 to 20 weeks to minimize gastrointestinal side effects. The calculator is designed for patients and healthcare providers who want a realistic preview of the weight loss journey, including the slow initial phase during dose escalation, the acceleration at therapeutic doses, the typical plateau at 60 to 72 weeks, and the expected weight regain if the medication is discontinued. It also models the impact of lifestyle factors (diet, exercise, baseline BMI) on the trajectory, drawing on subgroup analyses from the clinical trials. This tool does not replace medical advice. GLP-1 medications require a prescription, ongoing medical monitoring, and attention to potential side effects including nausea, vomiting, diarrhea, constipation, pancreatitis risk, and thyroid concerns. The calculator provides population-level estimates based on clinical trial averages; individual results vary significantly based on genetics, adherence, concurrent medications, and lifestyle factors.
Projected Weight at Week W = Starting Weight x (1 - Expected Cumulative Percent Loss at Week W / 100). Example: A patient starting at 230 pounds on semaglutide 2.4 mg (Wegovy) with a projected 15.0% total body weight loss at Week 68. At Week 16 (end of escalation): 230 x (1 - 3.5/100) = 221.95 lb. At Week 36: 230 x (1 - 10.0/100) = 207.0 lb. At Week 68: 230 x (1 - 15.0/100) = 195.5 lb. Total loss: 34.5 pounds over 68 weeks.
- 1The user enters baseline demographics: starting weight (pounds or kilograms), height, age, sex, and starting BMI (auto-calculated from weight and height). The calculator validates that the patient meets the FDA-approved indication criteria: BMI of 30 or greater, or BMI of 27 or greater with at least one weight-related comorbidity (type 2 diabetes, hypertension, dyslipidemia, or obstructive sleep apnea).
- 2The user selects the medication: semaglutide 2.4 mg (Wegovy), semaglutide 1.0 mg (Ozempic, used off-label for weight loss), tirzepatide 5 mg, 10 mg, or 15 mg (Zepbound/Mounjaro). Each medication has a distinct dose-escalation schedule and published efficacy curve. The calculator loads the corresponding trial data: STEP 1 through STEP 5 for semaglutide, SURMOUNT-1 through SURMOUNT-4 for tirzepatide.
- 3The dose-escalation schedule is displayed as a timeline. For semaglutide (Wegovy), escalation proceeds: 0.25 mg (weeks 1-4), 0.5 mg (weeks 5-8), 1.0 mg (weeks 9-12), 1.7 mg (weeks 13-16), 2.4 mg (week 17 onward). For tirzepatide (Zepbound), escalation proceeds: 2.5 mg (weeks 1-4), 5.0 mg (weeks 5-8), 7.5 mg (weeks 9-12), 10.0 mg (weeks 13-16), 12.5 mg (weeks 17-20), 15.0 mg (week 21 onward if tolerated). Weight loss during escalation is modest, approximately 2 to 5 percent of starting weight.
- 4The calculator models the weight-loss curve using a modified exponential decay function fitted to the published trial data. The curve shows rapid loss during weeks 16 through 40 (approximately 1.0 to 1.5 percent of body weight per month), gradual deceleration during weeks 40 through 60, and a plateau approaching the maximum effect between weeks 60 and 72. The STEP 1 trial showed semaglutide 2.4 mg producing a mean loss of 14.9 percent at week 68; SURMOUNT-1 showed tirzepatide 15 mg producing a mean loss of 22.5 percent at week 72.
- 5Lifestyle modifier inputs adjust the projection. Patients who combine the medication with a structured diet (500 kcal/day deficit) and exercise program (150+ minutes/week of moderate activity) typically achieve 2 to 4 percentage points more weight loss than medication alone. The STEP 3 trial, which combined semaglutide with intensive behavioral therapy, showed 16.0 percent weight loss versus 14.9 percent with medication alone. The calculator applies these modifiers to the base curve.
- 6A discontinuation scenario is optionally modeled. The STEP 1 extension study showed that patients who stopped semaglutide regained approximately two-thirds of the lost weight within one year of discontinuation. The calculator projects this regain trajectory, showing the expected weight at 6, 12, and 24 months post-discontinuation. This information helps patients and providers plan for long-term medication adherence or transition strategies.
- 7The output is a week-by-week chart showing projected weight, cumulative pounds lost, cumulative percent lost, current dose, and monthly cost at list price and with common insurance coverage tiers. A summary table highlights key milestones: 5 percent weight loss (the threshold for clinically meaningful health benefits), 10 percent (associated with significant metabolic improvement), 15 percent (associated with NAFLD resolution in many patients), and 20+ percent (achievable with tirzepatide 10-15 mg, associated with potential diabetes remission).
This patient's projected trajectory closely matches the STEP 1 trial mean. The first 16 weeks during dose escalation show modest loss (8.4 lb), followed by accelerated loss during weeks 16 through 48 (22 lb), then gradual deceleration to the plateau. The 15 percent loss moves her from Class II to Class I obesity and is expected to improve blood pressure, lipid profile, and insulin sensitivity.
Tirzepatide at the maximum 15 mg dose produces the largest weight losses seen in any GLP-1 trial. Combined with strong lifestyle adherence, this patient may exceed the trial average. The 70-pound loss eliminates approximately 10 BMI points, moving from Class III to Class I obesity. The SURMOUNT-1 trial showed that 36 percent of tirzepatide 15 mg patients achieved 25 percent or greater weight loss.
Ozempic at the 1.0 mg dose approved for diabetes produces less weight loss than the 2.4 mg Wegovy dose. The SUSTAIN trials showed approximately 9 to 11 percent weight loss with semaglutide 1.0 mg in diabetic patients. This patient achieves meaningful weight and glycemic improvement while taking a lower dose that may be more easily covered by diabetes insurance formularies.
The STEP 1 extension study demonstrated that approximately two-thirds of lost weight is regained within one year of stopping semaglutide, as the appetite-suppressing effects of the medication reverse. This finding underscores that GLP-1 medications treat obesity as a chronic condition requiring ongoing therapy, similar to how statins treat cholesterol or antihypertensives treat blood pressure.
Obesity medicine specialists and endocrinologists use timeline projections to set realistic patient expectations during the initial consultation. Showing patients the dose-escalation schedule and the corresponding slow early weight loss helps prevent discouragement and premature discontinuation. Patients who understand that the therapeutic effect begins at week 16 to 20 are more likely to persist through the gastrointestinal side effects of escalation.
Insurance companies and pharmacy benefit managers use weight-loss timeline data to establish prior authorization criteria and continuation rules. Many payers require documentation of at least 5 percent weight loss at 12 to 16 weeks as a condition for continued medication coverage. The calculator helps providers predict whether a patient is on track to meet these thresholds and when to submit continuation documentation.
Clinical trial designers and pharmaceutical researchers use published weight-loss curves from STEP and SURMOUNT to power new studies. Knowing the expected trajectory and variance at each time point allows accurate sample size calculations. The curves also serve as comparators for next-generation anti-obesity medications, including oral GLP-1 formulations, amylin analogs (cagrilintide), and combination therapies currently in Phase 2 and Phase 3 trials.
Patients use the calculator to plan practical aspects of their weight loss journey, including when to schedule clothing purchases (most patients drop 2 to 4 clothing sizes), when to expect improvements in sleep apnea symptoms (typically at 10 percent weight loss), when knee and back pain may improve (often at 5 to 8 percent), and when blood work should be repeated to assess metabolic improvements (typically at the 6-month mark).
Patients with type 2 diabetes consistently achieve less weight loss on GLP-1
Patients with type 2 diabetes consistently achieve less weight loss on GLP-1 medications than non-diabetic patients at the same doses. In the STEP 2 trial, semaglutide 2.4 mg produced 9.6 percent weight loss in diabetic patients versus 14.9 percent in the non-diabetic STEP 1 population. This is likely because insulin resistance and diabetes medications (especially insulin and sulfonylureas) create a hormonal environment that resists weight loss. The calculator adjusts projections downward by approximately 4 to 6 percentage points for patients with type 2 diabetes.
Patients who have previously undergone bariatric surgery and subsequently
Patients who have previously undergone bariatric surgery and subsequently regained weight may respond differently to GLP-1 medications. Limited data suggest that semaglutide produces meaningful additional weight loss (8 to 12 percent) in post-surgical patients, but the trajectory differs from the standard curve because these patients have altered gut anatomy and hormone profiles. The calculator flags post-bariatric status and applies modified projections based on emerging real-world data.
Concurrent medications that promote weight gain, including insulin,
Concurrent medications that promote weight gain, including insulin, sulfonylureas, thiazolidinediones, certain antidepressants (mirtazapine, paroxetine), antipsychotics (olanzapine, quetiapine), and corticosteroids, can blunt the weight-loss response to GLP-1 therapy. The calculator allows users to input concurrent medications and adjusts the projected weight loss downward by 1 to 5 percentage points depending on the medication's weight-gain potential. This information should prompt a conversation with the prescriber about possible medication substitutions.
| Medication | Trial | Dose | Duration | Mean % Weight Loss | Patients Achieving 20%+ Loss |
|---|---|---|---|---|---|
| Semaglutide (Wegovy) | STEP 1 | 2.4 mg/week | 68 weeks | 14.9% | 32% |
| Semaglutide (Wegovy) | STEP 2 (T2D) | 2.4 mg/week | 68 weeks | 9.6% | 10% |
| Semaglutide (Wegovy) | STEP 3 (+IBT) | 2.4 mg/week | 68 weeks | 16.0% | 36% |
| Semaglutide (Ozempic) | SUSTAIN 1-5 (T2D) | 1.0 mg/week | 30-56 weeks | 5.0-6.5% | N/A |
| Tirzepatide (Zepbound) | SURMOUNT-1 | 5 mg/week | 72 weeks | 15.0% | 27% |
| Tirzepatide (Zepbound) | SURMOUNT-1 | 10 mg/week | 72 weeks | 19.5% | 40% |
| Tirzepatide (Zepbound) | SURMOUNT-1 | 15 mg/week | 72 weeks | 22.5% | 50% |
| Tirzepatide (Mounjaro) | SURMOUNT-2 (T2D) | 15 mg/week | 72 weeks | 14.7% | 24% |
How much weight can I expect to lose on semaglutide?
In the STEP 1 trial, patients on semaglutide 2.4 mg (Wegovy) lost an average of 14.9 percent of their body weight over 68 weeks, compared to 2.4 percent with placebo. For a 230-pound person, this translates to approximately 34 pounds. However, individual results vary widely: about one-third of patients lose more than 20 percent, while another third lose less than 10 percent.
Is tirzepatide more effective than semaglutide?
In the SURMOUNT-1 trial, tirzepatide 15 mg produced a mean weight loss of 22.5 percent over 72 weeks, compared to the 14.9 percent seen with semaglutide 2.4 mg in STEP 1. However, these were different trials with different patient populations, not a head-to-head comparison. The SURMOUNT-5 trial directly compared tirzepatide 15 mg to semaglutide 2.4 mg and found tirzepatide produced statistically significantly greater weight loss.
What happens if I stop taking the medication?
The STEP 1 extension study showed that patients who discontinued semaglutide regained approximately two-thirds of their lost weight within one year. Appetite and food cravings return to pre-treatment levels within weeks of discontinuation. This is why obesity medicine experts increasingly view GLP-1 medications as long-term or indefinite therapy, similar to medications for other chronic conditions.
How long does the dose escalation take?
For semaglutide (Wegovy), dose escalation from 0.25 mg to the maintenance dose of 2.4 mg takes 16 weeks with four dose increases. For tirzepatide (Zepbound), escalation from 2.5 mg to the maximum 15 mg dose takes 20 weeks with five dose increases. The escalation can be slowed (staying at a tolerated dose longer) but should not be accelerated.
What are the most common side effects?
Gastrointestinal side effects are most common: nausea (40-44%), diarrhea (30%), vomiting (24%), and constipation (24%). These are typically most severe during dose escalation and improve over time. Serious but rare adverse events include pancreatitis (less than 0.5%), gallbladder disease (1-2%), and a theoretical thyroid tumor risk based on animal studies. Patients should report severe abdominal pain, persistent vomiting, or neck swelling immediately.
How much do these medications cost?
The list price is approximately $1,300 to $1,500 per month for both semaglutide (Wegovy) and tirzepatide (Zepbound) without insurance. With commercial insurance coverage, copays range from $25 to $500 per month depending on the plan. Medicare Part D has begun covering these medications for certain indications. Manufacturer savings programs can reduce costs for commercially insured patients. The high cost is a significant barrier to access.
Can I use this calculator for compounded semaglutide?
Compounded semaglutide products do not have the same clinical trial data supporting their efficacy and safety as FDA-approved branded products. Concentrations, purity, and bioavailability may differ. The calculator's projections are based on trials using FDA-approved formulations at verified doses. Results with compounded products may differ from the projected trajectories, and the FDA has issued warnings about safety concerns with compounded GLP-1 medications.
Pro Tip
To maximize your weight loss on a GLP-1 medication, focus on protein intake. Aim for at least 1.0 to 1.2 grams of protein per kilogram of ideal body weight per day. GLP-1 medications reduce appetite dramatically, and many patients inadvertently consume too little protein, which leads to greater muscle loss relative to fat loss. Preserving lean muscle mass during rapid weight loss is critical for maintaining metabolic rate and long-term weight maintenance.
Did you know?
The GLP-1 receptor agonist class was inspired by the Gila monster, a venomous lizard native to the American Southwest. In the 1990s, researcher John Eng discovered that a peptide in Gila monster venom (exendin-4) powerfully activated the human GLP-1 receptor. This discovery led to exenatide (Byetta), the first GLP-1 medication approved in 2005. Semaglutide and tirzepatide are synthetic analogs designed to last a full week in the body, but the class owes its existence to a desert lizard's saliva.
References
- ›Wilding, J. P. H., et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 384(11), 989-1002.
- ›Jastreboff, A. M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 387(3), 205-216.
- ›Rubino, D., et al. (2021). Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance (STEP 4). JAMA, 325(14), 1414-1425.