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 and Weight Loss — What You Need to Know
BMI (Body Mass Index) is a useful screening tool that healthcare professionals use to assess whether your weight is in a healthy range for your height. However, BMI and weight loss aren't directly linked — losing weight can improve your BMI, but BMI alone doesn't tell the full story about your health or fitness. This guide explains how BMI relates to weight loss, the NHS categories, and why other measurements matter too. Use our free BMI calculator above to check your personal BMI and see where you currently fall on the NHS health scale.
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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.
How BMI Works and NHS Weight Categories
BMI is calculated using a simple BMI formula: weight in kilograms divided by height in metres squared. The NHS uses this standard calculation to place adults into five categories. According to NHS BMI guidelines, a healthy BMI sits between 18.5 and 24.9. The bmi range uk also includes overweight (25–29.9), obese Class I (30–34.9), obese Class II (35–39.9), and severely obese (40+).
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower bmi categories uk thresholds because these groups face higher health risks at the same BMI level. Your GP can explain which category you fall into and what it means for your health. If you're working towards weight loss, knowing your starting BMI helps track progress over time — losing even 5–10% of your body weight can have meaningful health benefits.
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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 BMI is useful for population-level screening, it has important BMI limitations. BMI does not distinguish between muscle and fat — athletes or very fit people may have a high BMI but low body fat. BMI also ignores where fat is stored; waist circumference is actually a stronger predictor of cardiovascular risk. Use our free BMI calculator to get your number, but pair it with other measures: waist measurement (under 94cm for men, under 80cm for women is ideal), fitness level, and overall health markers like blood pressure and blood sugar.
Weight loss success isn't just about reaching a lower BMI number — it's about sustainable lifestyle changes, increased physical activity, and improved health outcomes. Track your progress with our free progress tracker as you work towards your goals.
- 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's the difference between overweight and obese BMI?
According to NHS guidelines, overweight BMI is 25–29.9, while obese Class I is 30–34.9. Obese Class II is 35–39.9, and severely obese is 40 and above. These categories help assess health risk — higher BMI generally correlates with increased risk of type 2 diabetes, heart disease, and other conditions. Your GP can explain what your specific BMI means for your health.
Can you lose weight without improving your BMI?
Yes. If you're gaining muscle while losing fat (through strength training), your weight might stay the same but your body composition improves. Conversely, weight loss alone may improve BMI, but overall fitness and health markers like blood pressure and cholesterol also matter. BMI is one tool, not the whole picture.
What's the healthy BMI range for UK adults?
The NHS defines healthy BMI as 18.5 to 24.9 for most UK adults. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9 because these groups have higher disease risk at the same BMI. Your GP can advise what's healthy for you personally.
How fast should you lose weight for health and BMI improvement?
The NHS recommends losing 0.5–1 kg per week for sustainable weight loss. This typically requires a calorie deficit of around 500 kcal per day. Faster weight loss can lead to muscle loss and is harder to maintain long-term. Sustainable changes to diet and activity are more likely to result in lasting BMI and health improvements.
Does BMI matter if you feel healthy and fit?
BMI is a screening tool, not a diagnosis. If you have a high BMI but are very fit with good blood pressure and cholesterol, your overall health may be good. However, BMI still indicates statistical health risk for your population group. Your GP can assess your individual health picture beyond just BMI — which is why personalised advice is important.
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.