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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What BMI Should I Be? NHS Guidelines Explained
Your ideal BMI depends on your height and health status, but the NHS recommends a healthy BMI range of 18.5 to 24.9 for most UK adults. However, the specific BMI you should aim for is individual and depends on factors including your age, ethnicity, muscle mass, and existing health conditions. This guide explains NHS BMI categories, how to find your personal healthy BMI range, and when to speak with your GP about your weight. Use our free BMI calculator above to check your personal BMI instantly, then read on to understand what your result means.
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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 Healthy Weight Ranges
The NHS BMI categories divide adults into five groups based on their BMI score. A healthy BMI falls between 18.5 and 24.9 according to standard NHS guidance. Below 18.5 is underweight, 25.0 to 29.9 is overweight, 30.0 to 34.9 is obese (Class I), 35.0 to 39.9 is obese (Class II), and 40.0 and above is severely obese (Class III).
However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds. For these groups, a healthy BMI range is 18.5 to 22.9, and overweight begins at 23.0. This is because these populations face higher health risks from excess weight at lower BMI levels.
To calculate your personal healthy weight range, multiply 18.5 by your height in metres squared for the lower bound, and 24.9 by the same figure for the upper bound. For example, at 1.73m tall (5ft 8in), the healthy range is approximately 55 to 75 kg (8st 10lbs to 11st 10lbs). Use the BMI calculator on this page to find your exact range instantly, without a UK pharmacy calculation.
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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 Support and When to Seek Help
The NHS provides a four-tier weight management pathway. Tier 1 includes self-help resources and community programmes available to all. Tier 2 involves primary care support from your GP, such as behaviour change advice and monitoring. Tier 3 is specialist multidisciplinary weight management services, where prescription medications like GLP-1 injections may be considered. Tier 4 is bariatric surgery for severe obesity with significant health complications.
You should speak with your GP if your BMI is above 25 and you have weight-related health conditions, or if your BMI is above 30. Your GP can assess your individual situation and refer you to appropriate support. Remember that BMI has limitations—it doesn't account for muscle mass, bone density, or fat distribution—so your GP may also consider your waist circumference and overall health picture when discussing your ideal weight.
- 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's the difference between my BMI and my healthy weight range?
Your BMI is a single number calculated from your height and weight. Your healthy weight range is the span of weights that give you a healthy BMI (18.5 to 24.9 for most adults). For example, at 1.70m tall, any weight between roughly 53 and 71 kg puts you in the healthy BMI range. Calculate both using the BMI calculator on this page.
Why do South Asian and Black adults have different BMI thresholds?
Research shows these populations have higher risks of type 2 diabetes, heart disease, and other conditions at lower BMI levels compared to white European populations. The NHS therefore recommends lower BMI thresholds (18.5 to 22.9 for healthy weight) to better reflect these health risks and catch weight-related problems earlier.
Should I aim for the middle of the healthy BMI range or the lower end?
There's no single "best" BMI—the healthy range of 18.5 to 24.9 is safe for most people. Your ideal weight depends on your individual factors including muscle mass, bone structure, age, and health conditions. Your GP can help you identify a realistic and healthy target weight based on your personal circumstances.
What does BMI not tell me about my health?
BMI doesn't distinguish between muscle and fat, so athletes may have high BMI but low body fat. It also ignores where fat is stored (belly fat is riskier than hip fat), doesn't account for age-related changes, and may be less accurate in elderly adults. The NHS recommends also measuring waist circumference and discussing overall health with your GP.
How do I use my BMI to set a weight loss goal?
Calculate your healthy BMI range using the formula or our free BMI calculator, then work backwards to your weight range. If you're overweight or obese, aiming for the upper end of the healthy range (around 24.9 BMI) is often more realistic than aiming for the lower end. Track progress with our free progress tracker and discuss realistic goals with your GP.
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.