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 Fast Do You Lose Weight on Mounjaro vs Wegovy?
Weight loss speed on Mounjaro depends on your dose, starting weight, diet, and activity level — there's no single answer. Clinical trials show average weight loss of 15–21% of body weight over 72 weeks with the prescription weight loss injection, though individual results vary significantly. Understanding how Mounjaro compares to Wegovy, another weekly weight loss injection, can help you and your GP decide which medication might suit you best. Both require a clinical assessment before prescription.
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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: Mounjaro vs Wegovy Weight Loss Speed
Mounjaro (tirzepatide) — SURMOUNT-1 trial results:
- 5 mg dose: average ~clinically studied weight loss (72 weeks)
- 10 mg dose: average ~clinically studied weight loss (72 weeks)
- 15 mg dose: average ~clinically studied weight loss (72 weeks)
Wegovy (semaglutide) — STEP-1 trial results:
- Maximum 2.4 mg dose: average ~clinically studied weight loss (68 weeks)
Mounjaro works as a dual GIP and GLP-1 receptor agonist, activating two hormone pathways to reduce appetite and support satiety. Wegovy is a GLP-1 agonist only, working through a single mechanism. Both are prescription-only weekly weight loss injections requiring a UK clinical assessment. The dose titration schedule — how quickly you reach maintenance dose — also affects how fast weight loss occurs. Try our GLP-1 weight loss calculator to explore projected outcomes at different doses.
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.
Weekly Weight Loss and Individual Variation
Most people lose weight gradually over weeks and months rather than days. Early weight loss may feel faster due to fluid loss when appetite reduces, but sustainable loss typically stabilises at around 0.5–1 kg per week. On a weekly weight loss injection like Mounjaro or Wegovy, you'll spend 4 weeks on each dose during titration, meaning speed may change as doses increase. Genetics, your starting weight, dietary adherence, and physical activity all significantly affect your personal weight loss speed. Your prescriber will monitor your progress and adjust doses accordingly. Some people reach their target weight; others plateau. Neither Mounjaro nor Wegovy assures specific outcomes. Track your progress over months, not days, for realistic expectations. Use our progress tracker to log your weight journey and see trends over time.
- 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.
Will I lose weight every week on Mounjaro?
Not necessarily at the same rate each week. Weight naturally fluctuates due to fluid retention, hormones, and meal timing. Most people see steady loss over 4–12 weeks rather than consistent weekly drops. Clinical trials measure results over months, not weekly. Your prescriber monitors overall progress at regular check-ups.
How does Mounjaro's dose affect weight loss speed?
Higher doses (10 mg and 15 mg) showed greater average weight loss in SURMOUNT trials than the 5 mg starting dose. However, reaching higher doses takes time — you spend at least 4 weeks on each dose before escalating. Speed also depends on how your body responds and whether you maintain dietary changes and activity.
Is Mounjaro faster than Wegovy for weight loss?
Clinical trials suggest Mounjaro's dual GIP+GLP-1 mechanism may produce slightly higher average weight loss than Wegovy's single GLP-1 mechanism, but individual results vary enormously. Your GP or prescriber can assess which is more suitable based on your health profile, not just potential speed.
Can I speed up weight loss on Mounjaro with stricter dieting?
Mounjaro works alongside dietary and lifestyle changes, not instead of them. A reduced-calorie diet combined with the medication may support faster initial loss, but very restrictive dieting is not recommended. The NHS advises losing 0.5–1 kg per week as a safe, sustainable rate.
What if I'm not losing weight on Mounjaro?
Some people lose weight more slowly or plateau despite the medication. This is normal and doesn't mean it's not working — appetite suppression and health improvements may continue. Your prescriber may adjust your dose or explore other factors. Always discuss any concerns at your regular check-ups with your GP or prescribing service.
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.