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
BMI Categories UK — What Do They Mean?
In the UK, BMI categories help you understand whether your weight is within a healthy range according to NHS guidelines. Your BMI (body mass index) is calculated using a simple formula based on your height and weight, and falls into one of five categories: underweight, healthy weight, overweight, obese, or severely obese. Understanding which category you fall into is a useful first step in assessing your health, though it's important to know that BMI has limitations and should be considered alongside other health measures. Use our free BMI calculator above to find your personal category instantly.
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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 divides adults into five clear categories based on their height and weight. Here are the official UK BMI categories:
- Underweight: BMI below 18.5 — may indicate insufficient body weight
- Healthy weight: BMI 18.5 to 24.9 — the target healthy BMI range for most adults
- Overweight: BMI 25.0 to 29.9 — overweight BMI threshold begins here
- Obese (Class I): BMI 30.0 to 34.9 — increased health risks
- Obese (Class II): BMI 35.0 to 39.9 — higher health risks
- Severely obese (Class III): BMI 40.0 and above — significantly elevated health risks
These BMI range UK categories apply to most adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the NHS recommends lower thresholds — a healthy BMI for these groups is 18.5 to 22.9, and overweight begins at 23.0. This is because these populations face higher risks of type 2 diabetes and cardiovascular disease 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.
BMI Limitations and What Else Matters
While the BMI calculator is a useful screening tool, it has important limitations. BMI doesn't distinguish between muscle and fat — athletes or very muscular individuals may have a high BMI but low body fat percentage. BMI also ignores where fat is stored; abdominal fat carries greater health risk than fat stored elsewhere. Age, ethnicity, and frame size also affect how BMI relates to actual health risk.
For a more complete picture, your GP may also measure your waist circumference. Men with a waist over 94cm (37 inches) or women over 80cm (31.5 inches) have increased health risks, regardless of BMI. Combining BMI assessment with waist measurement and other health markers gives a much clearer health picture than BMI alone.
- 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.
How do I calculate my BMI using the BMI formula?
The BMI formula is: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your BMI is 70 ÷ (1.75)² = 22.9, which falls in the healthy weight category. Use our free BMI calculator on this page for gradual improvement — just enter your weight and height.
What is the healthy BMI range according to NHS guidelines?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9 for most UK adults. 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 lower thresholds reflect higher health risks in these populations at standard BMI levels.
Why does BMI have limitations?
BMI doesn't account for muscle mass — someone very muscular might have a high BMI but low body fat. It also ignores where fat is stored (abdominal fat is riskier), and doesn't account for age, bone density, or ethnicity variations in health risk. BMI is a useful screening tool but works best alongside other health measures like waist circumference.
What should I do if my BMI falls in the overweight or obese category?
If your BMI is above 25, it's worth discussing with your GP. They can assess your overall health, family history, and any weight-related health conditions. Your GP may recommend lifestyle changes, refer you to a weight management programme, or in some cases, prescription weight loss support. Small changes often make a real difference.
Are the BMI categories different for children?
Yes — children's BMI uses age and sex-specific centile charts, not adult categories. The NHS uses the UK90 growth reference. If you're concerned about a child's weight, speak to your GP or health visitor, or use the NHS Healthy Weight Calculator for children, which provides age-appropriate guidance.
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.