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
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Average Weight Loss Per Week on Mounjaro
Clinical trials of Mounjaro (tirzepatide) show average weight loss of approximately 0.5 to 1.5 kg per week over the 72-week study period, though individual results vary significantly. The actual rate depends on your starting weight, dose, diet, activity level, and how your body responds to the medication. This guide covers the evidence-based data on Mounjaro weight loss, what NHS guidelines recommend, and the factors that influence your personal results.
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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.
Clinical Trial Data and Weight Loss Rates
The SURMOUNT-1 clinical trial, which tested Mounjaro in adults with obesity or overweight with weight-related conditions, showed average total weight loss of approximately 15–21% of body weight over 72 weeks (roughly one year). This translates to an average weekly loss of 0.5 to 1.5 kg depending on the dose used.
- 5 mg dose: ~clinically studied weight loss (~0.3–0.5 kg/week average)
- 10 mg dose: ~clinically studied weight loss (~0.6–1 kg/week average)
- 15 mg dose: ~clinically studied weight loss (~0.7–1.5 kg/week average)
Weight loss is not linear—most participants lost more in the first 3–4 months, then the rate slowed. These trials included reduced-calorie diet and increased physical activity, so medication alone does not account for all weight loss. Calculate your own GLP-1 weight loss projection using our free weight loss calculator.
Clinically BackedWeight Loss
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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.
Factors That Affect Your Personal Weight Loss Rate
Your individual weight loss on Mounjaro depends on several factors beyond the medication itself. Starting weight matters—people with higher initial weight often lose more kg per week initially. Age, metabolism, and genetics all influence results. Women and men may lose at different rates. Your adherence to diet and exercise is crucial; Mounjaro works best alongside a reduced-calorie diet and regular physical activity. Underlying health conditions like type 2 diabetes or PCOS may affect results. Dose escalation also matters—reaching your effective dose takes 16–20 weeks, so early weeks may show slower loss. Track your progress using our free progress tracker to monitor your personal trajectory.
- 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.
Is 0.5–1.5 kg per week weight loss normal on Mounjaro?
Yes. Clinical trials showed average loss in this range, but individual results vary significantly. Some people lose more, some less. Weight loss is not linear—expect faster loss initially, then slower rates. Consistency with diet and exercise affects outcomes. Your GP can review your personal progress.
How quickly will I lose weight on Mounjaro?
Most people see noticeable weight loss within the first 4–8 weeks as they reach their maintenance dose. However, Mounjaro's dose is increased gradually over 16–20 weeks, so early weeks may show modest loss. After reaching your target dose, weight loss typically continues at a steady rate for as long as you take the medication.
Why do people lose weight at different rates on Mounjaro?
Multiple factors affect rate: starting weight, metabolism, age, diet quality, exercise frequency, underlying health conditions, medication adherence, and genetics. Two people on the same dose may lose weight differently. This is normal. Your GP can help assess if your progress is appropriate.
Does the dose of Mounjaro affect how much weight you lose per week?
Yes. Clinical trials showed higher doses correlated with greater total weight loss. The 15 mg dose showed ~21% average loss versus ~15% at 5 mg. However, you start at a low dose (2.5 mg) and escalate gradually over weeks. You reach your maintenance dose at week 16–20, and loss typically accelerates once steady-state dosing begins.
Is losing weight on Mounjaro sustainable after you stop taking it?
Clinical evidence suggests weight loss is maintained during treatment. If treatment stops, weight can return, which is why Mounjaro is intended as an ongoing medication. Your GP will discuss whether long-term use is appropriate for your situation and when to review your treatment.
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.