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 UK BMI — NHS Guidelines
Your BMI (Body Mass Index) is a simple measurement that helps assess whether your weight is healthy for your height. In the UK, the NHS uses specific BMI categories and thresholds to guide health decisions. Understanding your personal BMI range and how it fits into NHS guidelines is an important first step in managing your health. This guide explains how the NHS defines healthy BMI, what different BMI categories mean, and when you should speak to your GP about your weight.
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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 divides your weight in kilograms by your height in metres squared (kg ÷ m²). The resulting number places you into one of five categories that guide NHS health recommendations.
According to NHS guidance, the standard BMI range uk categories are:
- Underweight: BMI below 18.5 — may need medical review
- Healthy weight: BMI 18.5 to 24.9 — the target range for most adults
- Overweight: BMI 25.0 to 29.9 — increased health risks begin
- Obese (Class I): BMI 30.0 to 34.9 — significant health concerns
- Obese (Class II): BMI 35.0 to 39.9 — higher health risks
- Severely obese (Class III): BMI 40.0 and above — serious health risks
Use our free BMI calculator above to find your personal BMI instantly and see where you fall within these NHS categories.
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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 and When to Seek Help
The NHS recognises that a healthy BMI is important for preventing type 2 diabetes, cardiovascular disease, and other weight-related conditions. If your BMI falls outside the healthy BMI range, your GP can discuss your individual health risks and what steps might help.
The NHS offers a structured weight management pathway through tier 1 (self-help and digital tools), tier 2 (GP-led programmes like the NHS Weight Loss Plan), and tier 3 (specialist services where prescription weight loss medication may be considered). Your GP is your first point of contact — they can assess your health, discuss your weight goals, and recommend the right support for you, whether that's lifestyle changes, structured programmes, or referral to specialist services.
- 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 a healthy BMI in the UK according to the NHS?
The NHS defines a healthy BMI as between 18.5 and 24.9 for most UK adults. If your BMI falls within this range, your weight is considered healthy for your height. However, the NHS also recognises individual variation — your GP can assess your personal health context beyond BMI alone.
Are BMI thresholds different for people from certain ethnic backgrounds?
Yes. The NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage because these groups face higher health risks at lower BMI levels. For these groups, overweight starts at BMI 23 and obesity at BMI 27.5, rather than the standard thresholds.
What BMI is considered overweight in the UK?
According to NHS guidelines, an overweight BMI threshold in the UK is 25.0 to 29.9. A BMI in this range suggests increased health risks, and your GP may recommend lifestyle changes or further health assessments depending on your individual circumstances.
Do BMI limitations mean I should ignore my BMI?
No. BMI is a useful screening tool, but it has BMI limitations — it doesn't distinguish between muscle and fat, doesn't account for age or where fat is stored, and may be less accurate for athletes or elderly people. Use your BMI alongside waist circumference and your GP's assessment for a complete picture.
How do I know if my weight is healthy for my height?
Use our free BMI calculator above to find your BMI instantly. If your result falls between 18.5 and 24.9, you're in the healthy range. Your GP can also discuss your weight and health in the context of your personal medical history, family background, and any health conditions you have.
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.