Free tool
GLP-1 muscle loss calculator
Across 36 trials, lean mass was a quarter to two-fifths of the weight lost. Answer four questions to see where in that range you probably sit, and what moves it. Nothing you enter leaves your browser.
Example: change the answers
3.3–3.9kg
33–39% of the 10 kg you lost. Upper end of the published range.
About 6.1 kg to 6.7 kg of the loss was fat.
- No strength training · pushes it up
Lean mass includes water and organ tissue, so the muscle part is smaller than this. Set your protein target or start the 12-week plan.
Read this first
What this number is, and what it isn't
It cannot see inside you
It applies an average from clinical trials to the number you type. Two people losing the same weight can land either side of the range.
Lean mass is not muscle
Body scans measure lean soft tissue, which includes water and organ tissue. We do not convert it into muscle, because the share varies between people and no fixed multiplier is honest.
The range is real, the middle is not a promise
24% to 39% is the confidence interval from the meta-analysis. We show the middle as a reference point, not a prediction about you.
It does not know what you have been doing
Protein intake, training and how fast you lost all change the split, and the published trials rarely measured them. That is why we show what changes it rather than adjusting the number.
What moves it
How to move the number
Protein
A 2025 expert consensus on GLP-1 care puts the target at 1.2 to 1.5 g per kg of body weight a day while you are losing weight. A 2025 US joint advisory quotes 1.2 to 1.6. Eating much less makes it easy to fall short, so it is worth working out your own number. Work out your target.
Strength training
The 2025 joint advisory says GLP-1 medicines should come with a structured exercise program including strength training at least three times a week. The WHO's general guideline for adults is at least two days a week. Free 12-week plan.
Checking, instead of guessing
A grip test, a chair-stand test or a DXA scan tell you far more than any estimate. How to check at home.
Questions
Muscle loss calculator FAQ
How much muscle do you lose on Ozempic or Mounjaro?
Across 36 randomised trials of 5,316 people, lean mass made up about 31% of the total weight lost, with a range of 24 to 39%. Lean mass is not the same as muscle: a body scan counts water and organ tissue in it too, so the muscle part is smaller than that.
Is lean mass the same as muscle?
No. Lean mass, or lean soft tissue, is everything that isn't fat or bone, which includes water and organs. Muscle is part of it, but the share varies a lot between people, so there is no honest way to convert one number into the other.
Is losing lean mass on a GLP-1 worse than losing it any other way?
Probably not by much. Recent reviews find the split looks similar to other fast weight loss, and in the SURMOUNT-1 sub-study the placebo group lost a similar proportion. What makes it worse in practice is eating too little protein and not training, which is what most people on these medicines do.
Can a calculator measure my muscle?
No, and neither can a bathroom scale. Only a body scan such as DXA, or a test of what you can actually do, gets close. This tool applies trial averages to your number so you know roughly what to expect.
How do I lose less lean mass?
Eat enough protein: a 2025 expert consensus on GLP-1 care recommends 1.2 to 1.5 g per kg of body weight a day while losing weight, and a 2025 US joint advisory quotes 1.2 to 1.6. Strength train: the joint advisory says at least three times a week for people on these medicines, and the WHO says at least two days a week for adults in general. And lose at a steadier pace rather than as fast as possible.
Sources
- Meta-analysis of 36 randomised trials (5,316 participants): lean mass loss was 31% of total weight lost, 95% CI 24–39%. Diabetes Metab Res Rev, June 2026. pmc.ncbi.nlm.nih.gov
- SURMOUNT-1 body-composition sub-study (tirzepatide): lean mass fell 10.9%, about a quarter of the weight lost, a similar proportion to the placebo group. pmc.ncbi.nlm.nih.gov
- STEP 1 body-composition sub-study (semaglutide): of 13.6 kg lost, about 5.3 kg was lean mass. N Engl J Med 2021;384:989–1002. nejm.org
- Mesinovic J et al. Exercise and dietary recommendations to preserve musculoskeletal health during weight loss in adults with obesity. Rev Endocr Metab Disord 2025. pmc.ncbi.nlm.nih.gov
- Sievenpiper JL et al. Nutritional and lifestyle supportive care recommendations for management of obesity with GLP-1-based therapies: an expert consensus statement using a modified Delphi approach. Obesity Pillars 2025. pmc.ncbi.nlm.nih.gov
- Bull FC et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med 2020;54:1451-1462. pubmed.ncbi.nlm.nih.gov
- Mozaffarian D et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory (ACLM, ASN, OMA, TOS). Obesity 2025. pmc.ncbi.nlm.nih.gov
The maths is public: how our calculators work, including what this one deliberately does not do.
General education for healthy adults, not medical advice. It is not a medical device and doesn't diagnose or treat anything.
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