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 Category — What Your NHS Weight Classification Means
Your BMI category tells you whether your weight falls into a healthy range according to NHS guidelines. The NHS uses five main BMI categories to classify adult weight: underweight, healthy weight, overweight, obese, and severely obese. Each category represents a different health risk level. However, BMI is a screening tool only — it doesn't account for muscle mass, where fat is stored, or individual circumstances. Understanding your BMI category is a helpful starting point, but your GP can provide personalised health advice based on your complete medical picture. Use our free BMI calculator above to check your category instantly.
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Calculate Your BMI Instantly
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 Health Classification
The NHS BMI formula is simple: your weight in kilograms divided by your height in metres squared. This calculation places you into one of five BMI categories that guide UK health recommendations.
- Underweight: BMI below 18.5 — may indicate insufficient nutrition or health concerns
- Healthy weight: BMI 18.5 to 24.9 — associated with lowest health risks according to NHS evidence
- Overweight: BMI 25.0 to 29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0 to 34.9 — significantly increased health risks
- Severely obese (Class III): BMI 40 and above — highest health risks requiring medical support
The healthy BMI range of 18.5 to 24.9 is based on research linking BMI levels to cardiovascular disease, type 2 diabetes, and other chronic conditions. However, BMI limitations are important to recognise — athletes may have high BMI despite low body fat, and muscle mass isn't distinguished from fat.
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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 Support and Your BMI Category
If your BMI category indicates overweight or obesity, the NHS offers a structured weight management pathway. Your GP can assess your individual health, discuss any weight-related conditions like high blood pressure or prediabetes, and refer you to appropriate support. For BMI over 30, or BMI 27–29 with weight-related health conditions, prescription weight management medications may be considered following NHS specialist assessment. The NHS recommends sustainable weight loss of 0.5 to 1 kg per week, achieved through a calorie deficit and increased physical activity. Our free progress tracker can help you log weight changes alongside lifestyle changes. Remember: your BMI category is one indicator among many — your GP provides the full health picture.
- 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 healthy BMI range according to NHS guidelines?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. However, people of South Asian, Chinese, Black African, and Black Caribbean descent have lower thresholds: 18.5 to 22.9 is healthy for these groups, reflecting their higher health risk at higher BMI levels. Your GP can advise what's healthy for you specifically.
What BMI category means I need to lose weight?
The NHS recommends weight management support if your BMI is 25 or above. For BMI 25–29 (overweight), lifestyle changes are usually recommended first. For BMI 30 and above (obese), or BMI 27–29 with weight-related health conditions, your GP may discuss medication options after specialist assessment. Check your category using our BMI calculator.
Does BMI account for muscle and fitness level?
No. BMI limitations include not distinguishing between muscle and fat, so very muscular or athletic people may have high BMI despite low body fat. BMI also ignores where fat is stored. Your GP uses BMI alongside waist measurement, fitness level, and medical history to assess your actual health risk.
How do I find out my BMI category?
Use our free BMI calculator on this page — enter your weight in stone, pounds, or kilograms, and your height in metres or feet. It instantly shows your BMI number and which NHS category you fall into, plus context about what it means for your health.
What happens if my BMI category is "obese"?
An obese BMI category means increased health risks. Your GP will discuss your individual circumstances, check for weight-related conditions like type 2 diabetes, and may refer you to NHS weight management services. Support ranges from lifestyle advice and digital tools, to specialist services and, in some cases, prescription medications.
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.