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 Can You Lose Weight on Mounjaro?
Weight loss speed on Mounjaro varies significantly between individuals, but clinical trial data provides realistic context. On average, people taking Mounjaro lost between 15% and 21% of their body weight over 72 weeks, though results depend on dose, diet, exercise, and individual metabolism. Unlike a quick-fix solution, Mounjaro works alongside lifestyle changes to support sustainable weight loss. It's a prescription-only weekly weight loss injection that requires a clinical assessment before being prescribed in the UK. Understanding the realistic timeframe helps set appropriate expectations and maintains motivation throughout treatment.
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.
Clinical Trial Data: Mounjaro vs Wegovy Weight Loss Speed
Mounjaro (tirzepatide) clinical results: In the SURMOUNT-1 trial, participants on Mounjaro lost an average of 15% body weight at 5mg dose, 19.5% at 10mg, and 20.9% at the maximum 15mg dose over 72 weeks (approximately 17 months). This is compared to approximately clinically studied weight loss in the placebo group. Wegovy (semaglutide) clinical results: In the STEP-1 trial, participants on Wegovy 2.4mg lost approximately 14.9% body weight over 68 weeks. Both injections work as GLP-1 receptor agonists, though Mounjaro is a dual GIP+GLP-1 agonist, meaning it activates two hormone pathways rather than one. This mechanism difference may explain slightly higher average weight loss on Mounjaro in head-to-head comparison, though individual results vary considerably. Weight loss typically becomes noticeable between weeks 4–8 as doses increase, with continued loss over several months when combined with reduced-calorie diet and increased physical activity.
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.
Realistic Weight Loss Timeline and Factors That Affect Speed
Most people experience noticeable weight loss within 4–8 weeks of starting Mounjaro, though this varies. A typical timeline involves dose escalation every 4 weeks (2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg), with weight loss gradual and steady rather than rapid. At each dose increase, appetite suppression typically strengthens, supporting further loss. Several factors influence your individual speed: starting weight (higher starting weight often means faster initial loss), adherence to reduced-calorie intake, exercise levels, age, metabolism, and whether you're taking other medications. Your prescriber will monitor your progress and adjust your dose or approach based on your response. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses, and our BMI calculator to track changes in your health metrics 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.
Is weight loss faster on Mounjaro than Wegovy?
Clinical trial data suggests Mounjaro may support slightly faster average weight loss (15–21% over 72 weeks vs approximately 15% for Wegovy), but individual results vary significantly. Speed depends more on your personal factors—diet adherence, exercise, starting weight, and metabolism—than on the medication alone. Your prescriber can advise which is more suitable for your circumstances.
How much weight can you lose per week on Mounjaro?
Average weight loss is approximately 0.5–1kg per week once you reach an effective dose, though this varies. The NHS recommends safe weight loss of 0.5–1kg weekly. Faster initial loss is possible in the first few weeks due to water loss, but sustainable loss typically follows this rate. Individual progress should be monitored by your prescriber.
Why is weight loss slower at the beginning of Mounjaro treatment?
Initial doses (2.5mg and 5mg) are starter and adjustment doses—they're lower than therapeutic doses. Weight loss accelerates as you progress through dose titration over 16–20 weeks. Once you reach an effective maintenance dose (typically 10mg or higher), appetite suppression increases and weight loss typically becomes more noticeable.
Can you lose weight faster on Mounjaro without a strict diet?
Mounjaro works best alongside a reduced-calorie diet and increased physical activity. While the medication supports reduced appetite, it doesn't replace the need for lifestyle changes. Clinical trials showed weight loss occurred in people who combined Mounjaro with dietary changes—medication alone is less effective without this support.
Is Mounjaro weight loss permanent after stopping treatment?
Weight loss achieved on Mounjaro can be maintained through ongoing lifestyle changes, but without continued medication and healthy habits, some weight regain is common. This is similar to other chronic condition medications—ongoing management supports ongoing results. Discuss long-term management with your prescriber.
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.