GLP-1 Weight Loss Calculator: Projection by Drug and Dose
Estimate average weight loss on a GLP-1 medicine — semaglutide (Wegovy, Ozempic) or tirzepatide (Zepbound, Mounjaro) — month by month, using the mean results of the published STEP, SURMOUNT and SUSTAIN trials. Results are trial averages, not a prediction for you and not medical advice. 100% private — nothing leaves your browser.
A GLP-1 weight loss calculator estimates how much weight an average adult loses on a GLP-1 medicine such as semaglutide or tirzepatide. It applies the mean percentage weight loss from a clinical trial of the chosen drug and dose to your starting weight and spreads it over the months of treatment. It shows a trial average, not a personal prediction.
How This GLP-1 Weight Loss Calculator Works
Choose a medicine and dose and the calculator looks up the mean weight change at the end of that dose’s main trial — for example 14.9% at week 68 for semaglutide 2.4 mg in STEP 1. It applies that percentage to your starting weight and fills in the earlier months with a smooth curve:
T is the trial length in weeks; after week T the projection is held flat, because the trial did not run longer. The constant k (0.04 per week for semaglutide, 0.045 for tirzepatide) is a modelling assumption, set so the curve passes close to two published checkpoints: in STEP 4, participants had lost 10.6% by week 20 and a further 7.9% of their week-20 weight by week 68; in SURMOUNT-4, the loss was 20.9% at week 36 and 25.3% at week 88. A 95 kg adult choosing semaglutide 2.4 mg for 12 months gets:
| Month | Projected weight | Lost so far | % lost |
|---|---|---|---|
| 1 | 92.6 kg | 2.4 kg | 2.5% |
| 3 | 88.8 kg | 6.2 kg | 6.5% |
| 6 | 85.2 kg | 9.8 kg | 10.3% |
| 9 | 83.0 kg | 12.0 kg | 12.6% |
| 12 | 81.7 kg | 13.3 kg | 14.0% |
Sex, age and activity level do not change the projection. The trials report one average per dose, so the calculator does not invent adjustments for them; those inputs only feed the calorie estimate.
Average Weight Loss by GLP-1 Drug and Dose
These are the trial results behind each option in the calculator. The percentages for the weight-management trials are each trial’s primary analysis, which counts everyone who was randomised, including people who stopped the medicine. The Ozempic (SUSTAIN) rows are on-treatment results reported in kg.
| Medicine and dose | Trial and length | Who was studied | Mean weight change | Comparison arm |
|---|---|---|---|---|
| Semaglutide 2.4 mg weekly (Wegovy) | STEP 1, 68 weeks | Obesity or overweight, no diabetes | −14.9% | Placebo −2.4% |
| Semaglutide 7.2 mg weekly (Wegovy) | STEP UP, 72 weeks (Wegovy prescribing information) | Obesity, no diabetes | −18.8% | 2.4 mg −15.5%; placebo −3.9% |
| Oral semaglutide 25 mg daily (Wegovy pill) | OASIS 4, 64 weeks | Obesity or overweight, no diabetes | −13.6% | Placebo −2.2% |
| Tirzepatide 5 / 10 / 15 mg weekly (Zepbound) | SURMOUNT-1, 72 weeks | Obesity or overweight, no diabetes | −15.0% / −19.5% / −20.9% | Placebo −3.1% |
| Tirzepatide 10 or 15 mg vs semaglutide 1.7 or 2.4 mg | SURMOUNT-5, 72 weeks (head-to-head) | Obesity, no diabetes | Tirzepatide −20.2% | Semaglutide −13.7% |
| Semaglutide 2.4 mg weekly (Wegovy) | STEP 2, 68 weeks | Type 2 diabetes, BMI 27 or more | −9.6% | Placebo −3.4% |
| Tirzepatide 10 / 15 mg weekly | SURMOUNT-2, 72 weeks | Type 2 diabetes, BMI 27 or more | −12.8% / −14.7% | Placebo −3.2% |
| Semaglutide 0.5 / 1 mg weekly (Ozempic) | SUSTAIN 7, 40 weeks | Type 2 diabetes, on metformin | −4.6 kg / −6.5 kg (about 4.7% / 6.8%) | Dulaglutide −2.3 kg / −3.0 kg |
| Semaglutide 2 mg weekly (Ozempic) | SUSTAIN FORTE, 40 weeks | Type 2 diabetes | −6.9 kg | Semaglutide 1 mg −6.0 kg |
The Ozempic percentages are our own conversion: the SUSTAIN 7 weight change in kg divided by the mean starting weight of each group (96.4 kg and 95.5 kg, from the ClinicalTrials.gov record). People with type 2 diabetes lost less on the same dose than people without it — 9.6% versus 14.9% on semaglutide 2.4 mg — which is why the calculator asks which group you are in.
Tirzepatide vs Semaglutide: What the Head-to-Head Trial Found
Four brand names cover two molecules. Ozempic and Wegovy are both semaglutide, a GLP-1 receptor agonist: Ozempic is approved for type 2 diabetes at up to 2 mg a week (Ozempic prescribing information), and Wegovy for weight reduction at a usual maintenance dose of 2.4 mg (Wegovy prescribing information). Mounjaro and Zepbound are both tirzepatide, which activates GIP as well as GLP-1 receptors: Mounjaro is approved for type 2 diabetes (Mounjaro prescribing information) and Zepbound for weight reduction at 5, 10 or 15 mg (Zepbound prescribing information).
SURMOUNT-5 compared the two directly in 751 adults with obesity and no diabetes. At 72 weeks the mean weight change was −20.2% with tirzepatide and −13.7% with semaglutide, and waist circumference fell by 18.4 cm versus 13.0 cm. In adults with type 2 diabetes, SURPASS-2 found tirzepatide 5, 10 and 15 mg reduced weight by 1.9, 3.6 and 5.5 kg more than semaglutide 1 mg over 40 weeks. These are group averages, not a recommendation: side effects, other conditions, cost and supply differ from person to person, so the choice is one for you and your prescriber.
How GLP-1 Medicines Cause Weight Loss
GLP-1 is a gut hormone that helps regulate appetite and calorie intake, and its receptors are found in areas of the brain involved in appetite regulation. Semaglutide binds to and activates those receptors; tirzepatide activates both GIP and GLP-1 receptors. Semaglutide also slows stomach emptying slightly and, when blood sugar is high, raises insulin release and lowers glucagon, which is how it lowers blood sugar in type 2 diabetes (Ozempic prescribing information). In the Wegovy weight-management trials everyone, including the placebo group, was also counselled to follow a diet about 500 kcal a day below their needs and to do at least 150 minutes of physical activity a week (Wegovy prescribing information), so the averages above include that support.
What to Expect Month by Month on a GLP-1
The dose is stepped up slowly to reduce stomach and bowel side effects: Wegovy rises every 4 weeks (0.25, 0.5, 1, 1.7 mg) and reaches its maintenance dose at week 17, and Zepbound starts at 2.5 mg and rises in 2.5 mg steps at least 4 weeks apart. Early loss is therefore modest. By week 20 the average loss on semaglutide in STEP 4 was 10.6%. Weight then levels off rather than falling forever: in STEP 5 the average at two years (15.2%) was about the same as at 68 weeks in STEP 1.
Stopping reverses much of it. In the STEP 1 extension, people who stopped semaglutide regained about two-thirds of their lost weight within a year, and in SURMOUNT-4 those switched from tirzepatide to placebo regained 14.0% over 52 weeks while those who continued lost a further 5.5%.
Calories and Protein While Taking a GLP-1
The calorie figure in your result is your estimated maintenance energy (the Mifflin-St Jeor equation multiplied by a conventional activity factor of 1.2 to 1.725) minus 500 kcal, the same deficit used in the Wegovy trials. The activity factor and the 1,200 kcal floor are simplifying assumptions. For protein, a 2025 joint advisory from four nutrition and obesity medicine societies notes that 1.2 to 1.6 g per kg of body weight per day has been proposed during active weight reduction, or an absolute target of 80 to 120 g a day. The advisory also warns that using actual body weight can overestimate needs in people with obesity, so treat the range as a starting point for a conversation with a dietitian. Lean sources include fish, poultry, eggs, yogurt, beans and lentils.
What This Calculator Cannot Tell You
- Your own response. In STEP 1, 83.5% of people on semaglutide lost at least 5% of their weight and 30.2% lost 20% or more (Wegovy prescribing information) — so roughly one in six lost less than 5%.
- Results outside the trial population. The weight-management trials enrolled adults with a BMI of 30 or more, or 27 or more with a weight-related condition.
- Side effects. Nausea and diarrhoea were the most common adverse events in STEP 1, and stomach and bowel effects led 4.5% of the semaglutide group to stop treatment.
- Whether a medicine is right for you. That is a decision for a qualified prescriber who knows your history.
Last updated: October 2026. Trial figures checked against PubMed abstracts, ClinicalTrials.gov records and current FDA prescribing information. For general information only — not medical advice.
Frequently Asked Questions
How accurate is this GLP-1 weight loss calculator?
It shows a trial average, not a personal prediction. The end figure for each drug and dose is the mean result of one published trial, for example 14.9% at 68 weeks for semaglutide 2.4 mg in STEP 1. Individual results spread widely: in STEP 1, 83.5% of participants lost at least 5% and 30.2% lost 20% or more, so roughly one in six lost under 5%. The month-by-month curve between the start and the end of the trial is a model assumption.
How much weight can I expect to lose on Ozempic?
Ozempic is approved for type 2 diabetes, not weight loss, and its trials enrolled people with diabetes. In SUSTAIN 7, semaglutide 0.5 mg and 1.0 mg lowered body weight by 4.6 kg and 6.5 kg on average after 40 weeks, from a starting weight of about 96 kg (roughly 5% and 7%). In SUSTAIN FORTE, the 2.0 mg dose averaged 6.9 kg at 40 weeks. The 0.25 mg dose is a four-week starting dose, not a maintenance dose.
What is the difference between Ozempic and Wegovy?
Both are once-weekly semaglutide injections. Ozempic is approved for type 2 diabetes, with maintenance doses of 0.5 mg, 1 mg or 2 mg. Wegovy is approved for weight reduction: the dose rises every 4 weeks (0.25, 0.5, 1 and 1.7 mg) and the maintenance dose from week 17 is 2.4 mg (recommended) or 1.7 mg, with 7.2 mg as the maximum. Wegovy also comes as a 25 mg daily tablet. In STEP 2, the 2.4 mg dose produced more weight loss than 1.0 mg in the same trial (9.9% versus 7.2%).
How does Mounjaro compare to Ozempic for weight loss?
Mounjaro (tirzepatide) acts on both GIP and GLP-1 receptors, while Ozempic (semaglutide) acts on GLP-1 only. In SURPASS-2, a 40-week trial in adults with type 2 diabetes, tirzepatide 5 mg, 10 mg and 15 mg reduced weight by 1.9 kg, 3.6 kg and 5.5 kg more than semaglutide 1 mg. In SURMOUNT-5, in adults with obesity but without diabetes, tirzepatide averaged 20.2% weight loss versus 13.7% for semaglutide at 72 weeks. Side effects in both groups were mainly gastrointestinal.
Why is protein important while taking GLP-1 medications?
Weight lost on these medicines includes lean tissue as well as fat, and a smaller appetite can make it hard to eat enough protein. A 2025 joint advisory from four nutrition and obesity medicine societies notes that 1.2 to 1.6 g of protein per kg of body weight per day has been proposed during active weight reduction, or an absolute target of 80 to 120 g per day. It also warns that using actual body weight can overestimate needs in people with obesity, so treat the range shown here as a starting point to discuss with a dietitian.
How long does it take to see results on GLP-1 medications?
Weight loss builds gradually because the dose is stepped up over the first 16 to 20 weeks. In STEP 4, participants had lost an average of 10.6% of their weight after 20 weeks on semaglutide. In SURMOUNT-4, participants who completed 36 weeks on tirzepatide had lost an average of 20.9%. Loss then levels off: in STEP 5, the average at two years (15.2%) was about the same as the 68-week result in STEP 1 (14.9%).
What happens if I stop taking GLP-1 medication?
Most of the lost weight tends to come back. In the STEP 1 extension, participants who stopped semaglutide after 68 weeks regained about two-thirds of the weight they had lost within one year (11.6 of 17.3 percentage points). In SURMOUNT-4, people switched from tirzepatide to placebo regained 14.0% over the next 52 weeks, while those who stayed on it lost a further 5.5%. Never stop or change a prescribed medicine without talking to your prescriber.
Which GLP-1 medication leads to the most weight loss?
In SURMOUNT-5, a head-to-head trial in adults with obesity and no diabetes, tirzepatide (10 or 15 mg) produced an average 20.2% weight loss at 72 weeks compared with 13.7% for semaglutide (1.7 or 2.4 mg). That is an average across a group, not a ranking for any one person: response, side effects, other health conditions, cost and insurance cover all differ, so the choice belongs with you and your prescriber.
How much weight can you lose on a GLP-1 in 3 months?
Less than the headline trial numbers, because the first three months are mostly spent stepping up the dose. This calculator estimates about 6.5% of starting weight at month 3 on semaglutide 2.4 mg and about 9.7% on tirzepatide 15 mg, which is around 6 kg and 9 kg for a 95 kg adult. Those month-3 figures come from the calculator curve, which is fitted to later trial checkpoints, so treat them as rough.