The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
How Much Weight Can I Lose on Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight loss injection that helped participants lose an average of 15–21% of their body weight in clinical trials — though individual results vary significantly. The amount you might lose depends on your starting weight, how well your body responds to the medication, and whether you combine it with diet and exercise changes. Your GP or prescriber can assess whether Mounjaro is suitable for you, and our free BMI calculator can help you understand your current weight status and what a healthy weight range looks like for your height.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Use Our BMI Calculator to Find Your Healthy Weight Range
Your BMI (body mass index) is a useful first step in understanding whether you're at a healthy weight for your height. According to NHS guidelines, a healthy BMI is between 18.5 and 24.9, and our free BMI calculator on this page instantly calculates yours and shows you your ideal weight range. Once you know your healthy weight range for your height, you can see exactly how much weight loss would move you into that range. For example, if you're currently 110 kg and your healthy weight range is 60–75 kg, you would need to lose approximately 35–50 kg to reach the upper end of a healthy weight. This gives you a concrete target, rather than relying on vague goals.
- Use the BMI calculator above to enter your current height and weight
- Note your current BMI category (underweight, healthy, overweight, obese)
- See your healthy weight range displayed instantly
- Calculate the difference between your current weight and your target range
- Remember that even losing 5–10% of your current weight has meaningful health benefits
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What Clinical Trials Show About Mounjaro Weight Loss
In the SURMOUNT-1 clinical trial, adults taking Mounjaro at the maximum dose of 15 mg lost an average of 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. At lower doses (5 mg and 10 mg), average weight loss was approximately 15% and 19.5% respectively. These are average figures — some people lost more, others less. Weight loss typically continues for the first year of treatment, and results depend on how consistently you follow dietary changes and take your injections as prescribed. Your GP or prescriber will monitor your progress and can adjust your dose if needed. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different Mounjaro doses based on your current weight.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
How much weight will I lose on Mounjaro?
Individual results vary significantly. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, alongside diet and exercise. Some people lose more, others less. Your prescriber can discuss realistic expectations based on your personal health and circumstances.
Is Mounjaro weight loss assured?
No. Mounjaro may help reduce appetite and support weight loss, but results depend on many factors including your individual metabolism, adherence to dietary changes, physical activity level, and how your body responds to the medication. It works best alongside lifestyle changes, not instead of them.
How long does it take to see weight loss results on Mounjaro?
Most people begin to notice appetite changes within the first 2–4 weeks, but significant weight loss typically becomes visible after 8–12 weeks of treatment at an effective dose. Weight loss continues gradually over the first year. Patience and consistency are important.
Can I use the BMI calculator to track my Mounjaro progress?
Yes. Use our free BMI calculator regularly (monthly, for example) to track changes in your BMI and see how you're progressing toward your healthy weight range. Our free progress tracker also allows you to log weight and monitor trends over time.
What if I don't lose weight on Mounjaro?
If you're not seeing weight loss after 12 weeks at an adequate dose, speak to your GP or prescriber. They may adjust your dose, review your diet and activity level, or discuss whether the medication is right for you. Some people don't respond well to GLP-1 medications — this is normal and doesn't mean you've failed.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.