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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BMI and Weight Loss: NHS Guidance for UK Adults
Your BMI (body mass index) is an important health screening tool that helps determine whether your weight falls into a healthy range. The NHS uses specific BMI categories to assess weight status and identify health risks. If you're overweight or obese, losing weight can significantly improve your health — but understanding your BMI is the first step. This guide explains how BMI relates to weight loss, what the NHS recommends, and how to access support. Use our free BMI calculator above to check your personal BMI instantly.
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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 What They Mean
The NHS BMI formula is straightforward: divide your weight in kilograms by your height in metres squared. This gives you a single number that fits into one of five categories according to NHS guidance.
- Below 18.5: Underweight — may need to gain weight for health
- 18.5 to 24.9: Healthy weight — lowest health risk
- 25.0 to 29.9: Overweight — increased health risk; weight loss recommended
- 30.0 to 34.9: Obese (Class I) — significantly increased health risk
- 35.0 to 39.9: Obese (Class II) — very high health risk
- 40.0 and above: Severely obese (Class III) — highest health risk
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — you may be at increased health risk even at a healthy BMI range by standard categories. Your GP can advise on your individual risk profile. Convert your weight between kg, stone, and lbs using the weight converter on this page to work out your measurements in whichever units you prefer.
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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 When to Seek Help
The NHS offers a structured weight management pathway with support at different levels. Tier 1 includes self-help resources, digital tools, and community programmes — this is where most people start. Tier 2 provides GP-led behaviour change support and structured weight loss programmes like the NHS Weight Loss Plan. Tier 3 is specialist multidisciplinary weight management services, where medication may be considered if lifestyle changes alone are not enough. Tier 4 covers bariatric (weight loss) surgery for severe obesity with significant health complications.
You should speak to your GP if your BMI is consistently above 25, you have weight-related health conditions like type 2 diabetes or high blood pressure, or you've tried to lose weight without success. Your GP can refer you to appropriate support and discuss whether prescription weight loss medication might be suitable for you.
- 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 limitations should I be aware of?
BMI doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. It also doesn't account for where fat is stored; abdominal fat poses greater health risks. BMI is less accurate for elderly people due to muscle loss, and may not apply during pregnancy. Use it as a screening tool alongside other health measures like waist circumference.
How much weight should I aim to lose per week?
The NHS recommends losing weight at a rate of 0.5 to 1 kg (1 to 2 lbs) per week for sustainable, healthy weight loss. This typically requires a calorie deficit of around 500 calories per day. Faster weight loss is possible with medical support but increases the risk of muscle loss and may not be sustainable long-term.
What's the difference between overweight and obese according to NHS categories?
According to NHS guidance, overweight is a BMI of 25.0 to 29.9, while obese starts at 30.0 and above. The overweight range indicates increased health risk, but obese categories (Class I, II, and III) carry significantly higher risks of serious health conditions including heart disease, stroke, and type 2 diabetes.
Can I access NHS weight loss medication?
Yes, prescription weight loss medications like tirzepatide (Mounjaro) and semaglutide (Wegovy) are available through NHS specialist tier 3 weight management services. You'll typically need referral from your GP and assessment by the specialist team. Availability and waiting times vary significantly by region, and medication is usually prescribed alongside lifestyle changes, not instead of them.
How does weight loss improve health outcomes?
Losing even 5 to 10% of your body weight can reduce blood pressure, improve blood sugar control, lower cholesterol, reduce joint pain, ease sleep apnoea, and lower your risk of certain cancers. Our GLP-1 weight loss calculator can help you estimate potential weight loss at different stages, giving you realistic targets to work towards with your healthcare team.
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.