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
What Is a Healthy BMI? NHS Guidelines for UK Adults
A healthy BMI (body mass index) is between 18.5 and 24.9 according to NHS guidance. BMI is a simple measure of your weight relative to your height and helps identify whether you're at a healthy weight, overweight, or obese. However, BMI has limitations—it doesn't account for muscle mass or where fat is stored—so it works best alongside other health measures like waist circumference. Use our free BMI calculator to check your personal BMI and see where you fall on the NHS scale.
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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 uses five standard BMI categories for adults across the UK:
- Underweight: BMI below 18.5—may indicate nutritional concerns; discuss with your GP if persistently underweight
- Healthy weight: BMI 18.5 to 24.9—associated with lowest health risks for most people
- Overweight: BMI 25.0 to 29.9—increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0 to 34.9—higher risk of type 2 diabetes and cardiovascular disease
- Obese (Class II & III): BMI 35.0 and above—significantly elevated health risks
Importantly, the NHS also recognises that South Asian, Chinese, Black African, and Black Caribbean adults have different BMI thresholds due to higher cardiovascular and metabolic risks at lower weights. For these groups, a healthy BMI starts at 18.5 but extends only to 22.9, and overweight begins at 23.0. These adjusted thresholds reflect evidence that excess weight poses greater health risks in these populations at lower BMI levels.
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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
If your BMI falls outside the healthy range, the NHS offers a structured four-tier weight management pathway. Tier 1 includes self-help tools and digital resources (such as the free calculators available here); Tier 2 provides primary care-based support through your GP surgery; Tier 3 involves specialist multidisciplinary weight management services for those needing intensive support; and Tier 4 covers bariatric surgery for severe obesity with serious health complications. Start by speaking to your GP about your weight and health goals. They can assess your individual situation, check for weight-related conditions like type 2 diabetes or high blood pressure, and refer you to appropriate support—whether that's a local weight management programme or prescription weight loss treatment if eligible. Even a modest clinically studied weight loss can meaningfully improve your health.
- 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 is the healthy BMI formula and how do I calculate it?
BMI is calculated using the formula: weight (kg) ÷ height (m)². For example, someone weighing 70kg and 1.75m tall would have a BMI of 70 ÷ (1.75)² = 22.9, which falls in the healthy range. You can calculate yours instantly using our free BMI calculator above.
Why does the NHS have different BMI thresholds for some ethnic groups?
Research shows that South Asian, Chinese, Black African, and Black Caribbean populations have higher risk of type 2 diabetes and heart disease at lower BMI levels compared to European populations. The NHS adjusted thresholds reflect this evidence—a healthy BMI for these groups ends at 22.9 rather than 24.9.
What are the limitations of BMI as a health measure?
BMI doesn't distinguish between muscle and fat—athletes may have a high BMI but low body fat. It also ignores where fat is stored (waist circumference matters) and may be less accurate for older adults or during pregnancy. Use BMI alongside waist measurement and discuss your personal health with your GP for full context.
I'm in the overweight category—what should I do?
First, book an appointment with your GP to discuss your weight and health. They can check for weight-related conditions, offer advice, and refer you to Tier 2 or Tier 3 NHS weight management services if appropriate. Even small lifestyle changes—like adding physical activity and reviewing diet—can help, and support is available.
Can a healthy BMI assures I'm healthy?
No. BMI is one screening tool but doesn't reflect overall health, fitness, blood pressure, cholesterol, or blood sugar levels. You can have a healthy BMI and still have health conditions, or a higher BMI and good health markers. Regular GP check-ups and open discussion about your individual health are essential.
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.