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 Health BMI — NHS Guidelines
Your BMI (body mass index) is a simple screening tool that helps you and your GP understand whether your weight is healthy for your height. The NHS uses BMI as a starting point to assess health risk, though it's important to know its limitations. This guide explains how the NHS defines healthy BMI ranges, who should measure their BMI, and what your results mean for your health. You can calculate your personal BMI instantly using our free BMI calculator above.
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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 Healthy Weight Ranges
The NHS defines healthy BMI as between 18.5 and 24.9 for most UK adults. BMI is calculated by dividing your weight in kilograms by your height in metres squared. Use our free BMI calculator on this page to find yours instantly.
The standard BMI categories used by the NHS are:
- Underweight: below 18.5 (may indicate health risks including bone loss)
- Healthy weight: 18.5–24.9 (associated with lower health risks)
- Overweight: 25.0–29.9 (increases risk of weight-related health conditions)
- Obese Class I: 30.0–34.9
- Obese Class II: 35.0–39.9
- Severely obese: 40.0 and above
However, BMI has important limitations. It doesn't distinguish between muscle and fat, doesn't account for where fat is stored (waist measurement matters too), and may be less accurate for athletes, elderly people, or during pregnancy. Ethnicity also affects health risk at the same BMI level.
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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 four-tier weight management pathway. Tier 1 includes self-help resources and community programmes. Tier 2 involves your GP and behaviour change support. Tier 3 is specialist multidisciplinary weight management services, where prescription medications like Mounjaro or Wegovy may be considered. Tier 4 includes bariatric surgery for severe obesity.
You should speak to your GP about weight management if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess your individual situation and signpost you to appropriate support. Even modest weight loss of 5–10% can significantly improve health markers. Track your progress with our free progress tracker to stay motivated.
- 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 NHS healthy BMI range?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. This range is associated with lower risk of weight-related health conditions. However, for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower healthy range of 18.5 to 22.9 due to higher health risks at the same BMI.
Should I use BMI as my only health measure?
No. BMI is a useful screening tool but has important limitations. The NHS recommends also measuring waist circumference — over 94cm (37 inches) for men or 80cm (31.5 inches) for women indicates increased health risk. BMI also doesn't account for muscle mass, fat distribution, or ethnicity-specific health thresholds. Speak to your GP for a complete assessment.
I have a BMI of 27 — should I see my GP?
If your BMI is 27–29.9 and you also have a weight-related health condition (such as type 2 diabetes, high blood pressure, heart disease, or sleep apnoea), the NHS recommends speaking to your GP about weight management support. Even without other conditions, a BMI above 25 warrants a discussion about healthy lifestyle changes.
What does the NHS offer for weight management?
The NHS weight management pathway includes tier 1 self-help resources, tier 2 GP-led behaviour change programmes, tier 3 specialist services (which may include prescription weight loss medications), and tier 4 bariatric surgery for severe obesity. Availability varies by region. Your GP can refer you to the appropriate tier based on your health needs.
Is the BMI formula the same for men and women?
Yes. The BMI formula is identical for men and women: weight (kg) divided by height (m) squared. However, NHS guidance acknowledges that men and women may carry fat differently and have different health risks at the same BMI. Additionally, lower BMI thresholds apply to certain ethnic groups regardless of gender, reflecting greater health risk at lower weights in those populations.
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.