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 BMI According to NHS Guidelines?
BMI (body mass index) is a simple measurement that helps assess whether your weight is healthy for your height. The NHS uses BMI as a key screening tool to identify whether adults are at a healthy weight, overweight, or obese. It's calculated by dividing your weight in kilograms by your height in metres squared. Understanding your BMI range according to NHS guidelines is the first step towards managing your health effectively, whether you're checking your current status or planning lifestyle changes.
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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 BMI formula uses the same calculation for all adults, and the results fall into clear categories that help you understand your health status:
- Underweight: BMI below 18.5 — may indicate nutritional concerns; discuss with your GP if persistently low
- Healthy weight: BMI 18.5 to 24.9 — the target healthy BMI range for most UK adults
- Overweight: BMI 25.0 to 29.9 — overweight BMI threshold indicates increased health risk; lifestyle changes recommended
- Obese (Class I): BMI 30.0 to 34.9
- Obese (Class II): BMI 35.0 to 39.9
- Severely obese (Class III): BMI 40.0 and above
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI categories are slightly different — healthy weight is BMI 18.5 to 22.9, and overweight starts at BMI 23.0. These adjusted thresholds reflect higher cardiovascular and diabetes risk in these populations at lower BMI levels. Use our free BMI calculator above to find your personal BMI instantly.
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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.
BMI Limitations and Other Health Measures to Consider
BMI has important limitations. It cannot distinguish between muscle and fat — athletes may have a high BMI but be very healthy. BMI also doesn't account for where fat is stored, which affects health risk. The NHS recognises these limitations and recommends measuring waist circumference alongside BMI for a fuller picture. Men with a waist over 94cm and women over 80cm face increased health risk. Your GP can discuss your individual health risks and recommend whether lifestyle changes, medical support, or referral to specialist weight management services would help.
- 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 according to the NHS?
For most UK adults, a healthy BMI is between 18.5 and 24.9. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a healthy BMI of 18.5 to 22.9. These guidelines reflect individual health risk at different weights.
How do I calculate my BMI?
BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your BMI is 70 ÷ (1.75 × 1.75) = 22.9. Our free BMI calculator above does this instantly — just enter your weight and height.
Is BMI accurate for everyone?
BMI is useful as a screening tool but has limitations. It cannot distinguish muscle from fat, so athletes may have a high BMI despite being healthy. It also doesn't account for age, bone density, or where fat is stored. Your GP can discuss whether BMI alone reflects your health risk.
What should I do if my BMI is in the overweight category?
If your BMI is 25.0–29.9, the NHS recommends lifestyle changes including balanced diet and regular physical activity. Your GP can offer support and may refer you to weight management services. Even a 5–clinically studied weight loss can improve health outcomes.
Do ethnicity-adjusted BMI thresholds apply to me?
Yes, if you identify as South Asian, Chinese, Black African, or Black Caribbean. These populations have higher cardiovascular disease risk at lower BMI levels. The NHS recommends discussing your personal risk factors with your GP, who can advise on appropriate interventions and monitoring.
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.