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 Does a BMI of 39 Mean?
A BMI of 39 places you in the obese category (Class II obesity) according to NHS guidelines. This means your weight carries increased health risks compared to the healthy weight range. The good news is that even modest weight loss can bring meaningful health improvements. Many people with a BMI of 39 are eligible for NHS support or prescription weight management options. Your GP can discuss personalised options with you, and you can use our free BMI calculator above to understand your specific situation in context.
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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.
BMI Categories and Where 39 Fits
The BMI formula divides your weight in kilograms by your height in metres squared. According to NHS BMI categories, a BMI of 39 falls into Class II obesity, which sits between 35.0 and 39.9. The full BMI range UK spans from underweight (below 18.5) through healthy weight (18.5–24.9), overweight (25.0–29.9), Class I obesity (30.0–34.9), Class II obesity (35.0–39.9), and severely obese (40.0+).
At a BMI of 39, you're just below the severely obese threshold. This category is associated with significantly increased risks of type 2 diabetes, cardiovascular disease, and certain cancers. The healthy BMI threshold starts at 18.5, meaning there is a meaningful gap between your current BMI and the overweight BMI threshold of 25.0.
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — in your case, you would still be in an elevated risk category. Use our BMI calculator above to see exactly where you sit and what your healthy weight range would be for your height.
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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 a useful screening tool recognised by the NHS, it has important BMI limitations. It doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. It also doesn't account for where fat is stored, which matters for health: fat around the stomach (visceral fat) poses greater cardiovascular risk than fat elsewhere.
Complementary measures include your waist circumference (for men, over 102cm indicates high risk; for women, over 88cm) and overall fitness level. Your GP may also check blood pressure, blood sugar, and cholesterol as part of a full health picture. Weight loss of just 5–10% of body weight can significantly improve blood sugar control, blood pressure, and cholesterol levels, even before reaching a healthy BMI.
- 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.
Is a BMI of 39 considered obese?
Yes, a BMI of 39 is classified as Class II obesity according to NHS guidelines. The obese category spans from 30 to 39.9, with 39 sitting in the upper part of that range. This classification indicates increased health risks compared to healthy weight, but many people at this BMI successfully lose weight with appropriate support.
What health risks are associated with a BMI of 39?
A BMI of 39 is associated with increased risk of type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea, certain cancers, and non-alcoholic fatty liver disease. However, these risks are not certain — they are statistical likelihoods. Weight loss can significantly reduce these risks.
What weight would I need to reach to have a healthy BMI?
Your healthy weight range depends on your height. For example, at 5ft 8in (173cm), a healthy BMI range would be approximately 55–74kg (8st 9lbs to 11st 8lbs). Use our free BMI calculator above to find your personal healthy weight range based on your actual height.
Can I lose weight with a BMI of 39?
Yes, weight loss is absolutely possible at a BMI of 39. The NHS recommends sustainable loss of 0.5–1kg per week through calorie deficit and physical activity. Many people are also eligible for prescription weight loss support through NHS specialist services or private prescribing. Discuss options with your GP.
What's the difference between BMI 39 and severely obese?
Severely obese (Class III) begins at a BMI of 40.0. At BMI 39, you're in Class II obesity. While the difference is just one BMI point, crossing 40 may trigger different eligibility thresholds for certain NHS treatments. Both categories carry meaningful health risks, and weight loss support 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.