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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Understanding BMI for Mounjaro on the NHS
If you're considering Mounjaro for weight management in the UK, BMI is the first step in determining NHS eligibility. The NHS uses specific BMI thresholds to identify adults who may benefit from prescription weight loss treatment, and understanding where you fall within the healthy BMI range can help you understand what options might be available through the NHS. Our free BMI calculator above can instantly calculate your personal BMI using your height and weight in UK measurements (stone, pounds, or kilograms). This guide explains the NHS BMI categories, how they relate to Mounjaro eligibility, and what the NHS weight management pathway looks like.
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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.
NHS BMI Categories and Mounjaro Eligibility
The NHS recognises five main BMI categories that guide weight management decisions, including whether prescription treatments like Mounjaro might be appropriate:
- Healthy weight: BMI 18.5–24.9 — generally no weight loss intervention needed
- Overweight: BMI 25.0–29.9 — may benefit from lifestyle support; prescription treatment only if weight-related health conditions present
- Obese (Class I): BMI 30.0–34.9 — eligible for specialist weight management support including potential prescription treatment
- Obese (Class II): BMI 35.0–39.9 — eligible for specialist services; Mounjaro may be considered
- Severely obese (Class III): BMI 40.0+ — eligible for comprehensive specialist assessment including medication and bariatric surgery discussion
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds due to increased health risk at these weights: healthy weight is 18.5–22.9, and overweight begins at 23.0. Use our weight converter to check your weight in different units and understand your position within these ranges.
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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.
NHS Weight Management Pathway and Mounjaro Access
The NHS offers a tiered weight management pathway. Tier 1 includes self-help and community programmes; Tier 2 involves primary care-based support from your GP. Mounjaro is typically prescribed through Tier 3 specialist weight management services, which you access via GP referral. Your GP will assess whether specialist referral is appropriate based on your BMI, health conditions, and previous weight loss attempts.
NICE has approved tirzepatide (Mounjaro) for NHS use in specialist weight management services for adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions such as type 2 diabetes, cardiovascular disease, or hypertension. However, NHS availability varies significantly by region and waiting times can be substantial. Our GLP-1 weight loss calculator can help you understand potential outcomes with Mounjaro alongside your BMI category.
- 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.
What BMI do I need to be eligible for Mounjaro on the NHS?
The NHS typically considers Mounjaro for adults with a BMI of 30 or above. If your BMI is 27–29.9, you may be eligible if you have weight-related health conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. For South Asian, Chinese, or Black African/Caribbean adults, lower thresholds apply (BMI 27.5+). Your GP will assess your individual eligibility.
How is BMI calculated and what are its limitations?
BMI is calculated as weight (kg) divided by height (m) squared. While it's a useful screening tool, BMI has limitations — it doesn't distinguish between muscle and fat, doesn't account for where fat is stored (waist circumference matters too), and may be less accurate for elderly people or very muscular individuals. The NHS recommends using BMI alongside other health measures.
Will the NHS definitely prescribe Mounjaro if my BMI is above 30?
Not necessarily. BMI is just one factor. Your GP will consider your overall health, any weight-related conditions, previous weight loss attempts, and whether specialist tier 3 services are available in your area. Even if you meet BMI criteria, NHS access depends on regional availability and capacity — waiting times can be very long in many areas.
What's the difference between NHS and private Mounjaro access based on BMI?
Both NHS and private routes assess your BMI and health, but the NHS focuses on clinical need through a specialist pathway with a GP referral. Private prescribing through online pharmacies may have different assessment criteria and can be accessed without NHS referral, though you still require a clinical assessment from a licensed prescriber.
Can I use my BMI to calculate what weight loss to expect from Mounjaro?
No — BMI alone doesn't predict individual weight loss outcomes. Clinical trials showed average weight loss of 15–21% of body weight, but results vary significantly between individuals. Your age, metabolism, starting weight, diet, activity level, and adherence all affect outcomes. Try our free GLP-1 weight loss calculator for a personalised projection estimate.
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.