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 to Percentile in NHS Context
BMI percentiles compare your individual BMI against the wider population, but in the NHS context, what matters most is your absolute BMI category and your personal health. Unlike percentiles used in children's health (which account for age and sex-specific growth patterns), adult BMI categories are standardised across the population. The NHS uses fixed BMI ranges to assess health risk, rather than percentile rankings. Understanding where your BMI falls within NHS guidelines helps you recognise whether your weight poses health risks and when to seek support from your GP or specialist services.
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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 a straightforward BMI formula and categorises adult weight status into five bands. Your BMI is calculated as weight (kg) divided by height (m) squared, or using our free BMI calculator above for gradual improvement.
- Underweight: BMI below 18.5 — may indicate nutritional concerns
- Healthy weight: BMI 18.5–24.9 — associated with lower health risks
- Overweight: BMI 25–29.9 — increased risk of weight-related conditions
- Obese Class I: BMI 30–34.9 — significant health risks emerge
- Obese Class II: BMI 35–39.9 — higher cardiovascular and metabolic risk
- Severely obese: BMI 40+ — serious health implications
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds due to higher risk at lower weights. A healthy BMI for these groups starts at 18.5 but extends only to 22.9, with overweight beginning at 23.
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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 Act
If your BMI falls into the overweight or obese range, the NHS recommends speaking to your GP as a first step. Your GP can assess your individual health, discuss bmi limitations (such as muscle mass not being accounted for), and recommend appropriate support. The NHS operates a four-tier weight management pathway: tier 1 includes self-help and community programmes; tier 2 involves primary care interventions; tier 3 offers specialist multidisciplinary services where prescription medications may be considered; tier 4 covers bariatric surgery for severe obesity with significant comorbidities.
Even modest weight loss of 5–10% of your body weight can improve blood pressure, blood sugar control, and joint health. Use our free weight converter to track your progress in familiar UK measurements.
- 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 BMI percentile and NHS BMI category?
BMI percentiles rank your weight against the general population, commonly used for children's growth monitoring. NHS adult categories use fixed BMI ranges (18.5–24.9 healthy, 25–29.9 overweight, etc.) regardless of percentile. The NHS focuses on absolute health risk categories, not population ranking.
Does a higher BMI percentile always mean health risk?
Not necessarily a direct correlation. A high BMI percentile indicates a higher weight relative to others, but health risk depends on your absolute BMI category. Someone at BMI 26 (75th percentile) faces different risks than BMI 32. Individual health factors, fitness, and waist circumference also matter significantly.
Can I have a healthy BMI but still need weight management support?
Yes. Even within the healthy BMI range, factors like waist circumference, fitness level, family history, and existing health conditions matter. Your GP can advise whether lifestyle changes or medical support would benefit your individual health, regardless of BMI percentile.
Why does the NHS use BMI categories instead of percentiles for adults?
BMI categories provide consistent, evidence-based health risk thresholds across all adults. Percentiles vary depending on the population studied, making them less useful for clinical decision-making. The NHS prefers standardised categories aligned with cardiovascular and metabolic risk research.
How accurate is BMI if I'm very muscular or athletic?
BMI does not distinguish muscle from fat, so athletic individuals may have high BMI despite low body fat. This is a key BMI limitation. If you're very fit or muscular, discuss your actual health risk with your GP, who may assess waist circumference, fitness level, and medical history for a fuller picture.
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.