GLP-1 weight loss calculator
What the trials found, at your starting weight
Showing the average trial participant until you change something. The weight is 105.4 kg, the baseline mean printed on the Wegovy label; the height is ours, chosen to land near the trial’s mean BMI of 37.9. The label reports mean weight and mean BMI separately and you cannot derive either from the other, which is why the figure below reads 37.8 rather than matching exactly. The percentages further down were measured in people of roughly this build.
BMI is a screening ratio of weight to height. It does not measure body fat, and it does not distinguish muscle from fat — which is why an athlete and a sedentary person of the same build can share a number that means different things. It is here for one narrow reason: the FDA indications below are written in BMI, so it is the unit the eligibility question is actually asked in. Centers for Disease Control and Prevention
What the labels say about a BMI of 37.8
- Wegovyon BMI alone
Indicated at BMI 30+, or 27+ with at least one of: hypertension, type 2 diabetes, dyslipidaemia.
The indication, quoted
Wegovy is indicated as an adjunct to a reduced calorie diet and increased physical activity for chronic weight management in adult patients with an initial body mass index (BMI) of 30 kg/m2 or greater (obesity) or 27 kg/m2 or greater (overweight) in the presence of at least one weight-related comorbid condition (e.g., hypertension, type 2 diabetes mellitus, or dyslipidemia).
- Zepboundon BMI alone
Indicated at BMI 30+, or 27+ with at least one of: hypertension, dyslipidaemia, type 2 diabetes, obstructive sleep apnoea, cardiovascular disease.
The indication, quoted
Zepbound is indicated as an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in adults with an initial body mass index (BMI) of 30 kg/m2 or greater (obesity) or 27 kg/m2 or greater (overweight) in the presence of at least one weight-related comorbid condition (e.g., hypertension, dyslipidemia, type 2 diabetes mellitus, obstructive sleep apnea or cardiovascular disease).
Meeting a label indication is not the same as being prescribed the drug, and neither is the same as an insurer paying for it. Those are three separate gates and this tool only reads the first. What insurers actually cover is a different question with a worse answer.
The results, translated onto 232 lb
These are the published proportions of trial participants who reached each threshold, in both arms, from the FDA prescribing labels. They are not a forecast for you.
Zepbound 15 mg weekly
SURMOUNT-1 (Study 1, NCT04184622) · 630 on the drug, 643 on placebo · 72 weeks
- Lost at least 5%12 lb for you
- Lost at least 10%23 lb for you
- Lost at least 15%35 lb for you
- Lost at least 20%46 lb for you
9.1% of the people given this drug did not reach even 5%. That is roughly one in 11. Nothing published tells you in advance which group you would be in — that is what a distribution means, and it is the part a single predicted number deletes.
Intention-to-treat: every randomised patient, including those who stopped the drug. Missing week-72 weights were imputed from retrieved dropouts.
ZEPBOUND (tirzepatide) injection — Prescribing Information, Table 3 — U.S. Food & Drug Administration
Zepbound 10 mg weekly
SURMOUNT-1 (Study 1, NCT04184622) · 636 on the drug, 643 on placebo · 72 weeks
- Lost at least 5%12 lb for you
- Lost at least 10%23 lb for you
- Lost at least 15%35 lb for you
- Lost at least 20%46 lb for you
11.1% of the people given this drug did not reach even 5%. That is roughly one in 9. Nothing published tells you in advance which group you would be in — that is what a distribution means, and it is the part a single predicted number deletes.
Intention-to-treat: every randomised patient, including those who stopped the drug. Missing week-72 weights were imputed from retrieved dropouts.
ZEPBOUND (tirzepatide) injection — Prescribing Information, Table 3 — U.S. Food & Drug Administration
Zepbound 5 mg weekly
SURMOUNT-1 (Study 1, NCT04184622) · 630 on the drug, 643 on placebo · 72 weeks
- Lost at least 5%12 lb for you
- Lost at least 10%23 lb for you
- Lost at least 15%35 lb for you
- Lost at least 20%46 lb for you
14.9% of the people given this drug did not reach even 5%. That is roughly one in 7. Nothing published tells you in advance which group you would be in — that is what a distribution means, and it is the part a single predicted number deletes.
Intention-to-treat: every randomised patient, including those who stopped the drug. Missing week-72 weights were imputed from retrieved dropouts.
ZEPBOUND (tirzepatide) injection — Prescribing Information, Table 3 — U.S. Food & Drug Administration
Wegovy 2.4 mg weekly
STEP 1 (Study 1) · 1,306 on the drug, 655 on placebo · 68 weeks
- Lost at least 5%12 lb for you
- Lost at least 10%23 lb for you
- Lost at least 15%35 lb for you
- Lost at least 20%46 lb for you
Not reported on this label. The trial’s journal publication gives a figure, but against a different population definition, so merging the two would make the row look complete rather than make it true.
16.5% of the people given this drug did not reach even 5%. That is roughly one in 6. Nothing published tells you in advance which group you would be in — that is what a distribution means, and it is the part a single predicted number deletes.
Intention-to-treat: every randomised patient, including those who stopped the drug. Missing week-68 weights were imputed from retrieved subjects in the same arm.
WEGOVY (semaglutide) injection — Prescribing Information, Table 7 — U.S. Food & Drug Administration
Wegovy 2.4 mg weekly
STEP 2 (Study 2) · 404 on the drug, 403 on placebo · 68 weeks
- Lost at least 5%12 lb for you
- Lost at least 10%23 lb for you
- Lost at least 15%35 lb for you
- Lost at least 20%46 lb for you
Not reported on this label. The trial’s journal publication gives a figure, but against a different population definition, so merging the two would make the row look complete rather than make it true.
32.6% of the people given this drug did not reach even 5%. That is roughly one in 3. Nothing published tells you in advance which group you would be in — that is what a distribution means, and it is the part a single predicted number deletes.
Intention-to-treat: every randomised patient, including those who stopped the drug. Missing week-68 weights were imputed from retrieved subjects in the same arm.
WEGOVY (semaglutide) injection — Prescribing Information, Table 7 — U.S. Food & Drug Administration
And what happened when people stopped
Every figure above is measured while the drug is still being taken. This is the same question asked at the other end, which is the half the calculators leave out.
STEP 4 (Study 4 on the Wegovy label)
Everyone took semaglutide for a 20-week run-in. The 803 who reached 2.4 mg were then randomised either to continue or to switch to placebo, and followed to week 68.
+16 lb regained at your weight, if you tracked the group that stopped — 6.9% of body weight over 48 weeks after randomisation.
−18 lb over the same period in the group that continued — -7.9%. That gap is what the drug was doing.
Both groups had already lost the same weight on the same drug before they were split, so the 14.8-point spread between them is about as clean a measurement of what stopping costs as this field has. The label adds its own caveat: because people who could not tolerate the titration never reached randomisation, these results describe people who had already got on with the drug.
WEGOVY (semaglutide) injection — Prescribing Information, Table 7 — U.S. Food & Drug Administration
STEP 1 trial extension
A 327-participant subset of STEP 1 completers was followed for a further year after both the drug and the lifestyle programme were withdrawn at week 68.
+27 lb regained at your weight, if you tracked the group that stopped — 11.6% of body weight over 52 weeks after withdrawal (week 68 to week 120).
No comparison arm. Nobody in this study kept taking the drug, so there is nothing to set the figure above against.
This subset had lost 17.3% of their body weight by week 68. A year after stopping they had regained about two-thirds of it, leaving them a net 5.6% below where they started — still ahead, but a long way from where they finished. The cardiometabolic improvements measured alongside the weight loss reverted towards baseline for most of the variables too, which is the part that matters beyond the scales.
Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension — Diabetes, Obesity and Metabolism (Wilding et al.)
Direct answer
What you need to know
Evidence strength: StrongThis tool will not tell you how much weight you will lose, because that number does not exist yet. What exists is a distribution. In SURMOUNT-1, 56.7% of people on tirzepatide 15 mg lost at least 20% of their body weight and 9.1% did not reach even 5% — same drug, same dose, same 72 weeks. The tool above shows you every one of those outcomes at your starting weight, with the placebo arm beside each.
Key takeaways
- Mean weight change was -20.9% on tirzepatide 15 mg and -14.9% on semaglutide 2.4 mg — against -3.1% and -2.4% on placebo.
- Roughly 1 in 6 people on semaglutide, and 1 in 11 on tirzepatide 15 mg, did not reach a 5% reduction at all.
- Around a third of the placebo groups also lost 5% or more. Everyone in these trials got a diet and exercise programme.
- Both labels indicate at BMI 30+, or 27+ with a weight-related condition.
Important limitation: These are trial populations with a mean BMI of about 38, screened for eligibility, excluded for various conditions, and supported with dietary counselling and a 150 minute-a-week activity target throughout. You are one person and not a population, and nothing published can tell you where in the distribution you would land.
Next action: If the numbers make you want to go further, the question that follows is what it costs to stay on one — which our cheapest-routes comparison prices with the membership fee added to the medication rather than advertised separately.
Primary sources: FDA — Zepbound label, FDA — Wegovy label
General education, not medical advice. This tool reads published labels; it does not assess you, and it cannot tell you whether a medication is appropriate for you.
Why this tool refuses to give you one number
Search for a GLP-1 calculator and you will find a dozen that ask your weight and return a single figure: you could lose 38 lbs. The arithmetic behind that is not wrong. It takes a trial’s mean percentage and multiplies. The problem is what the mean is.
A mean is a property of a population — in STEP 1, 1,306 people over 68 weeks. It is the balance point of a spread that runs from people who lost nothing to people who lost a third of their body weight. Handing one person the balance point and calling it their result converts a distribution into a promise, and the promise is the part that is false.
The mean is real. Applying it to one person is not measurement, it is a rounding error with your name on it.
So this page shows the responder distribution instead: the published proportion of participants who reached each threshold, which is a thing the trials actually counted. Translating those onto your own weight invents nothing. It tells you the shape of the range you would be entering, which is the honest answer to the question you asked.
The placebo column, and why it is never optional
In STEP 1, 31.1% of the placebo group lost at least 5% of their body weight. They received no semaglutide. What they received was the same reduced-calorie diet and the same activity programme as everybody else in the trial, plus 68 weeks of being watched by a research team.
That number is the single most clarifying figure on this page, and you will not find it on a page selling you the drug. The medication’s contribution is not the height of the first bar. It is the gap between the two bars — and the gap is still large, which is the point. Semaglutide roughly tripled the share of people reaching a 5% reduction and multiplied the share reaching 15% by ten. Showing the comparator does not weaken the case for these drugs. It is the only way to state the case accurately.
Which number you are being shown, and by whom
There are two ways to report a weight-loss trial, and they give different answers to the same question.
| Estimand | Who it counts | Result | Who leads with it |
|---|---|---|---|
| Intention-to-treat | Every person randomised, including those who stopped the drug or dropped out | −20.9% | The FDA label, and this page |
| Efficacy estimand | People as they would do if they stayed on treatment throughout | −22.5% | The manufacturer’s release, and most coverage of it |
Neither is a trick. But if you have not started a GLP-1, you have not yet found out whether you are someone who tolerates it, and 15.1% of the tirzepatide 15 mg group discontinued the study drug. The intention-to-treat figure includes them. It is the number that answers the question a person asks before they start, so it is the number this tool uses throughout.
What the tool cannot do
- It cannot tell you where you would land. No published model does. Age, sex, starting BMI, diabetes status and dose all shift the average outcome, but none of them narrows an individual result to a point.
- It cannot assess you. Contraindications, a personal or family history of medullary thyroid carcinoma, pregnancy, pancreatitis, and interactions with other medications are all real reasons a clinician might say no, and none of them are things a web page can check.
- It cannot tell you what you will be charged. Meeting a label indication, being prescribed a drug, and having it covered are three separate gates. The coverage page deals with the third.
- It does not apply to compounded products. Every figure here comes from a trial of a specific approved product. See compounded semaglutide for why that distinction is legal rather than cosmetic.
Common questions
How much weight will I lose on a GLP-1?
Nobody can tell you, and any tool that answers this with one number is telling you something it does not know. What is knowable is the distribution: in SURMOUNT-1, 56.7% of people on tirzepatide 15 mg lost at least 20% of their body weight, 70.6% lost at least 15%, and 9.1% did not reach even 5%. Those are four different outcomes from the same trial, drug and dose. The tool above translates each of them onto your starting weight so you can see the actual spread rather than its midpoint.
Why does this calculator show a placebo column?
Because a responder rate on its own does not tell you what the drug did. In STEP 1, 31.1% of the placebo group also lost at least 5% of their body weight — they were on a reduced-calorie diet and an exercise programme, which is what the trial gave everybody. The drug's contribution is the gap between the two bars, not the height of the first one. Marketing pages show one bar.
Do I qualify for Wegovy or Zepbound?
Both are indicated at a BMI of 30 or above, or 27 or above with at least one weight-related condition — the labels name hypertension, dyslipidaemia and type 2 diabetes, and Zepbound's also names obstructive sleep apnoea and cardiovascular disease. The tool checks your BMI against both thresholds and quotes the indication. Meeting it is not the same as being prescribed the drug, and neither is the same as your insurer paying for it.
Is BMI a good measure for this?
Not for describing your health, no. It is a ratio of weight to height that does not measure body fat and cannot distinguish muscle from fat. It is on this page for one narrow reason: the FDA indications are written in BMI, so it is the unit the eligibility question is actually asked in. For deciding whether these drugs are appropriate for you, it is a starting point for a conversation, not a verdict.
Why do your figures differ from the ones I have seen elsewhere?
Because we use the FDA label, which reports the intention-to-treat population — everyone randomised, including people who stopped taking the drug. Press releases and much of the coverage lead with the efficacy estimand, which conditions on staying on treatment and is systematically more flattering. For tirzepatide 15 mg the gap is 20.9% against 22.5%. If you have not started yet, you have not yet decided to persist, so the intention-to-treat figure is the one that answers your question.
What happens if I stop taking it?
In the Wegovy label's own withdrawal study, the group switched to placebo after 20 weeks on the drug regained 6.9% of their body weight over the following 48 weeks, while the group that continued lost a further 7.9%. In the STEP 1 extension, a subset followed for a year after everything was withdrawn had regained about two-thirds of what they lost. These medications are studied and labelled for chronic weight management, which means the results above describe people who were still taking them.
Do these numbers apply to compounded semaglutide or tirzepatide?
No. Every figure on this page comes from a trial of a specific FDA-approved product at a specific dose. A compounded preparation is not that product, was not in these trials, and has not been reviewed by the FDA for potency or consistency. Whether it performs the same way is unknown rather than assumed.
Sources
Each source below supports specific statements on this page. We cite the strongest available authority and verify against the current version before publishing.
- ZEPBOUND (tirzepatide) injection — Prescribing InformationU.S. Food & Drug AdministrationSupports: Table 3 — the intention-to-treat mean weight change and the proportions reaching 5%, 10%, 15% and 20% reduction at week 72 for tirzepatide 5, 10 and 15 mg and for placebo — and the indication wording quoted in the tool.
- WEGOVY (semaglutide) injection — Prescribing InformationU.S. Food & Drug AdministrationSupports: Table 7 — the same figures at week 68 for semaglutide 2.4 mg in Studies 1 and 2 — Table 8, the withdrawal result from Study 4, and the indication wording. This label reports no 20% threshold, which is why the tool shows that row as absent.
- Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extensionDiabetes, Obesity and Metabolism (Wilding et al., 2022)Supports: What happened to a 327-participant subset of STEP 1 completers in the year after both the drug and the lifestyle programme were withdrawn.
- About Adult BMICenters for Disease Control and PreventionSupports: The adult BMI formula and the standard weight-status categories.
- Drug approvals, labeling and safety communicationsU.S. Food & Drug AdministrationSupports: That a compounded preparation is not the product these trials tested, and carries none of these results.
This page is general education, not medical advice. Talk to your own healthcare provider about your situation before starting, stopping, or changing any medication.