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 Quickly Do You Lose Weight With Mounjaro?
Weight loss with Mounjaro (tirzepatide) is not immediate — most people begin to see changes around week 4–6 after starting treatment. Clinical trials show an average weight loss of 15–21% of body weight over 72 weeks, depending on the dose and how closely diet and exercise changes are followed. Weight loss is gradual and individual results vary significantly. In the UK, Mounjaro is available through NHS specialist tier 3 weight management services or via private prescription, following a clinical assessment by a licensed healthcare professional.
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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.
Weight Loss Timeline and NHS Eligibility
Mounjaro is a prescription-only weekly weight loss injection that works by reducing appetite and supporting feelings of fullness. In the SURMOUNT-1 clinical trial — the main UK and international trial — participants achieved average weight loss of approximately 15% at 5mg, 19.5% at 10mg, and 20.9% at 15mg over 72 weeks (around 18 months). However, weight loss begins gradually: most people notice no significant change in the first 2–3 weeks, with modest changes becoming visible around weeks 4–6. The dose titration process takes at least 16 weeks (you start at 2.5mg and increase by 2.5mg every 4 weeks until reaching your effective maintenance dose).
For NHS access, you must be referred to a tier 3 specialist weight management service by your GP. NICE guidance approves Mounjaro for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Eligibility is slightly lower for South Asian, Chinese, Black African, and Black Caribbean patients (BMI 27.5+). NHS availability varies by region — some areas have significant waiting lists.
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.
Private vs NHS Routes and Realistic Expectations
If NHS waiting times are too long, Mounjaro is available through private online prescription services following an online clinical assessment. Both routes require a licensed prescriber to confirm you meet eligibility criteria. Weight loss success depends on three factors: the medication itself, consistent reduced-calorie diet, and increased physical activity. Our GLP-1 weight loss calculator can help you estimate potential results at different doses based on your current weight. Remember that weight loss is not linear — you may lose weight quickly one week and plateau the next. Using our free progress tracker, you can log weekly weigh-ins and see your overall trend over time, which is more useful than obsessing over daily numbers.
- 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 per week on Mounjaro?
Average weight loss is approximately 0.5–1 kg per week at therapeutic doses, but this varies considerably between individuals. Some people lose more in the first month, then plateau. The clinical trial average was 20.9% total body weight over 72 weeks at the maximum 15mg dose — roughly 0.25–0.5 kg weekly on average, though your own rate may differ.
When do you start losing weight on Mounjaro?
Most people see no noticeable change in the first 2–3 weeks. Modest weight loss typically becomes visible around weeks 4–6 as your body adjusts to the medication. Since you titrate the dose every 4 weeks (2.5mg → 5mg → 7.5mg etc.), more significant loss often occurs once you reach your effective maintenance dose.
Is Mounjaro available on the NHS in the UK?
Yes. NICE approved Mounjaro for NHS use in specialist tier 3 weight management services. Eligibility requires a BMI of 30+ or 27–29.9 with weight-related health conditions. You must be referred by your GP. Availability and waiting times vary significantly by region and ICB (integrated care board).
How does Mounjaro compare to Wegovy for weight loss speed?
In clinical trials, Mounjaro (tirzepatide) achieved slightly higher average weight loss (20.9%) than Wegovy/semaglutide (around 15%) at maximum dose. However, individual results vary widely. The choice depends on eligibility, availability, cost, and prescriber recommendation rather than assured speed differences.
Can I speed up weight loss with a higher Mounjaro dose?
Higher doses (up to 15mg maximum) produce greater average weight loss in clinical trials, but they also increase side effects like nausea and gastrointestinal upset. Your prescriber will titrate you slowly to find the best balance between efficacy and tolerability. Faster is not always better — sustainable loss is the goal.
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.