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 Your BMI and Mounjaro Eligibility Under NHS Guidance
Your BMI is an important starting point for understanding your weight health under NHS guidelines. If you're considering Mounjaro or exploring weight management options, knowing your personal BMI and how it fits into NHS categories helps you understand what support may be available. This guide explains NHS BMI thresholds, how Mounjaro fits into the NHS weight management pathway, and what steps to take if you're interested in treatment options.
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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.
NHS BMI Categories and Mounjaro Eligibility
According to NHS guidelines, a healthy BMI for most UK adults is between 18.5 and 24.9. Your BMI calculator results place you in one of these NHS-recognised categories: underweight (under 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), obese class I (30.0–34.9), obese class II (35.0–39.9), or severely obese (40.0+).
For Mounjaro prescription eligibility through NHS specialist services, you typically need a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, NHS guidance recommends lower thresholds — eligibility may start at BMI 27.5 or above, because these groups face higher health risks at lower BMI levels.
It's important to understand that BMI has limitations. It doesn't distinguish between muscle and fat, so athletes may have a high BMI but low body fat. BMI also doesn't account for where fat is stored — waist circumference matters too. Your GP can provide personalised context about what your BMI means for your individual health.
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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 Next Steps
The NHS offers a four-tier weight management pathway. Tier 1 includes self-help tools and community programmes. Tier 2 involves primary care support and behaviour change programmes. Tier 3 is specialist multidisciplinary weight management services — this is where prescription medications like Mounjaro may be considered. Tier 4 covers bariatric surgery for severe obesity.
To access Mounjaro through the NHS, you'll typically need a referral from your GP to a tier 3 specialist service. NHS access to Mounjaro varies significantly by region and availability, and waiting lists can be lengthy in many areas. Your GP can assess whether you're eligible and arrange a referral. If NHS options have limited availability in your area, private prescription options are also available through online clinical assessments with UK-licensed prescribers.
- 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?
Generally, a BMI of 30 or above, or 27–29.9 with a weight-related health condition like type 2 diabetes or high blood pressure. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply (27.5+). Your GP can advise on your personal eligibility based on your health profile.
How do I check my personal BMI using NHS standards?
Use our free BMI calculator on this page to enter your height and weight in kg, stone, or lbs. The calculator shows your BMI instantly and compares it to NHS healthy weight ranges. You can also use the NHS BMI healthy weight calculator on the NHS website for additional context.
Does a high BMI automatically mean I need weight loss treatment?
Not necessarily. BMI is a screening tool but has limitations — it doesn't show body composition or muscle mass. Your GP considers your overall health, not BMI alone. Even modest weight loss (5–10% of body weight) can bring health benefits. Your GP can discuss whether treatment is right for you.
What's the difference between NHS and private access to Mounjaro?
NHS access is through specialist tier 3 weight management services following GP referral — availability and waiting times vary by region. Private access is through online clinical assessment with UK-licensed prescribers, available without NHS referral but at personal cost. Both routes require prescription and clinical assessment.
Can I use the weight converter to understand my BMI better?
Yes. Our free weight converter helps you switch between kg, stone, and lbs — useful if you know your weight in one unit but need it in another. Combined with our BMI calculator, it gives you a complete picture of your weight in NHS terms and your personal BMI category.
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.