Mounjaro Weight Loss Calculator
This planning tool projects how much weight you could lose over a chosen number of weeks, using conservative, moderate, or ambitious assumptions. Results vary between individuals.
Thinking about starting Mounjaro and wondering what weight loss might look like for you? This calculator gives you a personalised projection based on your starting weight, timeframe, and the pace of loss you select.
It uses percentage-based weekly loss assumptions — not a fixed number of kilograms — which is more realistic because people with more weight to lose tend to lose more in absolute terms.
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What this calculator does
This calculator projects your weight week by week based on the scenario you choose (conservative, moderate, or ambitious). It shows milestones, estimated total loss, your BMI before and after, and how long it might take to reach a target weight.
Who it is for
Adults in the UK considering or already using Mounjaro (tirzepatide) for weight loss, who want to understand what a realistic trajectory might look like. Also useful for GP conversations and personal planning.
How to use it
Enter your current weight, height, age, sex, and activity level. Choose a timeframe (e.g. 24 weeks) and a weight-loss scenario. Optionally enter a target weight to see how long it could take to reach.
How the calculation works
We apply a weekly percentage loss to your body weight each week (compounding, so each week's loss is based on the updated weight). Conservative = 0.5%/week, Moderate = 0.75%/week, Ambitious = 1%/week. These ranges are informed by clinical trial outcomes for tirzepatide but are simplified planning assumptions — not medical predictions.
Worked example
Starting at 95 kg, moderate scenario (0.75%/week), 24 weeks: Week 1 loss = 0.71 kg, Week 24 projected weight ≈ 79.2 kg, total loss ≈ 15.8 kg (16.6%). A conservative scenario would project ≈ 10.7 kg loss; ambitious ≈ 20.4 kg.
Assumptions and limitations
- Weekly loss rates are simplified planning assumptions, not medical predictions
- Real-world results depend on dosage, adherence, diet, exercise, and individual metabolism
- The calculator does not model dose titration, plateaus, or regain
- BMI is calculated using the standard formula (weight / height²) and has known limitations
- This is not medical advice — always discuss treatment with a qualified clinician
Frequently asked questions
How much weight can you lose on Mounjaro?
Clinical trials showed average weight loss of 15–22.5% of body weight over 72 weeks at the highest dose. Individual results vary significantly. This calculator lets you explore different scenarios based on your starting weight.
How quickly does Mounjaro work?
Most people begin to notice weight loss within the first few weeks, though the rate varies. Doses are typically increased gradually over several months. This calculator projects loss from week 1 for planning purposes.
Is this calculator medically accurate?
No — this is a planning and educational tool, not a medical prediction. It uses simplified assumptions based on clinical trial data. Your actual results will depend on many individual factors. Always discuss your treatment plan with a healthcare provider.
What weight-loss scenario should I choose?
If you are unsure, start with 'moderate'. Conservative is a gentler assumption; ambitious reflects the upper end of trial outcomes. Your prescriber can help you set realistic expectations.
Related calculators
- BMI Calculator for Mounjaro — Find your BMI, see which category it falls into, and understand how it relates to eligibility criteria for treatments like Mounjaro.
- Mounjaro Calorie Calculator — Calculate your maintenance calories and a safe deficit range to support steady weight loss alongside Mounjaro treatment.
- Mounjaro Calorie Deficit Calculator — Enter your maintenance calories and a target intake (or desired weekly loss) to see the size of your deficit and projected weight change ove
- Mounjaro Protein Calculator — Find out how much protein you should aim for each day and per meal to support muscle preservation during weight loss on GLP-1 medication.
- Mounjaro vs Wegovy Calculator — Enter your weight and the monthly costs of each medication to compare projected weight loss, total spend, and cost per kilogram lost over yo
Related guides
- How Much Weight Can You Lose on Mounjaro? — A realistic look at expected weight loss on Mounjaro (tirzepatide), based on clinical trial data and practical planning advice.
- Mounjaro vs Wegovy for Weight Loss — A balanced comparison of Mounjaro (tirzepatide) and Wegovy (semaglutide) — mechanism, effectiveness, cost, and side effects.
- How Much Protein Should You Eat on Mounjaro? — Why protein matters during GLP-1 weight loss and how to hit your daily target with practical meal guidance.
- How Many Calories Should You Eat on Mounjaro? — Understanding your calorie needs during Mounjaro treatment — maintenance, deficit, and safe intake ranges explained.
- What BMI Means for Weight-Loss Injections — How BMI is used to assess eligibility for weight-loss medications like Mounjaro and Wegovy, and its limitations.
Sources and references
SURMOUNT-1 trial (Jastreboff et al., NEJM 2022), NICE TA1026 tirzepatide guidance, Mifflin-St Jeor BMR equation
Last updated
Last reviewed: 2025-04-12.