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 31 Mean?
A BMI of 31 falls into the obese category according to NHS guidelines, which classifies BMI 30.0–34.9 as obese (Class I). This means your weight is above the healthy range for your height, and this can increase risks for several health conditions. However, BMI is just one screening tool — it doesn't account for muscle mass, overall fitness, or where fat is stored. Your GP can help you understand what a BMI of 31 means specifically for your individual health and discuss weight management options that may be right for you.
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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.
Health Implications of a BMI of 31
At a BMI of 31, research shows increased health risks compared to the healthy weight range (BMI 18.5–24.9). These risks include:
- Type 2 diabetes: Risk increases significantly at this BMI level
- Cardiovascular disease: Heart attack and stroke risk rise with excess weight
- High blood pressure: Often develops or worsens above BMI 30
- Sleep apnoea: More common at higher BMI levels
- Joint problems: Additional weight places strain on knees, hips, and spine
- Certain cancers: Obesity is linked to 13 types of cancer
Even modest weight loss — just 5–10% of your current weight — can improve these health markers and reduce disease risk. Use our free BMI calculator to check your current status and track changes over time.
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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.
Weight Management Options in the UK
If you have a BMI of 31, the NHS recommends exploring lifestyle changes first, including balanced diet and regular physical activity. If lifestyle changes alone aren't sufficient, prescription weight loss medications may be an option. These are available through NHS specialist weight management services or private online prescribing following clinical assessment.
Medications like Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1 receptor agonists licensed in the UK for weight management. In clinical trials, Mounjaro helped participants lose an average of 15–21% of body weight, whilst Wegovy showed around 15% average loss — though individual results vary significantly. Your GP can refer you to specialist services to discuss whether medication is appropriate for your circumstances, or you can seek a private clinical assessment.
- 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 the NHS?
The NHS defines healthy BMI as 18.5 to 24.9. At BMI 31, you are above the healthy range. However, for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — healthy BMI starts at 18.5 and goes to 22.9 for these groups due to higher health risks at lower BMI levels.
Can I lose weight through diet and exercise alone at BMI 31?
Yes, many people successfully lose weight through sustainable calorie deficit and increased physical activity. The NHS recommends losing 0.5–1 kg per week for lasting results. A calorie deficit of around 500 kcal daily typically achieves this. Our free progress tracker can help you log weight loss over time. However, if lifestyle changes plateau, your GP can discuss additional support or medication options.
Am I eligible for prescription weight loss medications at BMI 31?
At BMI 31, you likely meet eligibility criteria for weight loss medications in the UK. You can discuss options with your GP, who may refer you to NHS specialist weight management services, or you can seek a private clinical assessment from a UK-licensed prescriber. Eligibility depends on your overall health, any weight-related conditions, and individual circumstances.
How much weight could I lose with Mounjaro or Wegovy at BMI 31?
Clinical trials showed average weight losses of 15–21% with Mounjaro and around 15% with Wegovy. These results were achieved alongside a reduced-calorie diet and increased physical activity. Individual results vary — some people lose more, some less. Our GLP-1 weight loss calculator can help estimate potential loss at different doses, but actual outcomes depend on many personal factors including adherence and lifestyle changes.
Is my BMI of 31 considered obese, and what does that mean?
Yes, according to NHS guidelines, a BMI of 31.0–34.9 is classified as obese (Class I). This is a clinical classification, not a personal judgment. It simply indicates that your weight is above the healthy range for your height and carries increased health risks. Many people at this BMI live healthy lives, but discussing health and weight with your GP is worthwhile to identify any personalized risk factors and appropriate support options.
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.