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
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How Do You Calculate Your Weight and BMI in the UK?
Calculating your weight, BMI, and healthy weight range is straightforward once you know the right formulas and UK measurements. Whether you're converting between kilograms, stone, and pounds, or working out your BMI using NHS guidance, understanding these calculations helps you track your health effectively. This guide explains the key formulas used in the UK and how to apply them to your own health data.
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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.
Key Weight and BMI Calculation Formulas
BMI calculation: The formula is weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your BMI would be 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy weight range according to NHS guidance.
Converting kg to stone: Divide your weight in kg by 6.35029. So 70kg ÷ 6.35 = 11 stone. To also show pounds, multiply the decimal by 14: 70kg = 11 stone and 0.1 pounds.
Converting kg to lbs: Multiply your weight in kg by 2.20462. So 70kg × 2.20462 = 154.3 lbs. Use our free weight converter above to switch between metric and imperial measurements instantly.
Healthy weight range: Calculate this by multiplying height (m)² by 18.5 (lower) and 24.9 (upper). At 1.75m, the healthy range is 56.6kg to 76.3kg (8st 13lbs to 12st).
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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.
UK Health Guidance and BMI Categories
According to NHS guidance, BMI categories in the UK are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), and obese (30.0 and above). However, adults of South Asian, Chinese, Black African, or Black Caribbean heritage face higher health risks at lower BMI levels, so the NHS recommends lower thresholds: healthy weight 18.5–22.9, overweight 23.0–27.4, and obese 27.5 and above.
Remember that BMI is a screening tool but has limitations—it doesn't account for muscle mass or where fat is stored. Try our free BMI calculator on this page to check your personal BMI instantly, and speak to your GP about what your result means for your individual health.
For practical health tracking, use our free BMI calculator above to work out your BMI in seconds, and the weight converter to switch between kg, stone, and lbs. If you're interested in weight management strategies—including lifestyle changes or prescription options like GLP-1 medications—our GLP-1 weight loss calculator can help you estimate potential outcomes based on current clinical evidence. Your GP can provide personalised advice about what your weight measurements mean and what healthy weight management looks like for you.
- 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 in the UK?
Use the formula: weight (kg) ÷ height (m)². For example, 70kg ÷ (1.75 × 1.75) = BMI of 22.9. According to NHS guidance, this falls in the healthy weight range. Use our free BMI calculator above for gradual improvement.
How do I convert kilograms to stone?
Divide your weight in kg by 6.35029. So 70kg ÷ 6.35 = 11 stone. To also show pounds, multiply the decimal portion by 14. Our weight converter above does this instantly for any weight.
What is a healthy weight range according to NHS guidance?
The healthy BMI range is 18.5–24.9. Calculate your range by multiplying height (m)² by 18.5 (lower) and 24.9 (upper). For example, at 1.75m tall, the healthy range is 56.6kg to 76.3kg. Your GP can discuss what's healthy for you individually.
Are BMI calculations the same for all ethnic backgrounds in the UK?
No. The NHS recommends lower BMI thresholds for South Asian, Chinese, Black African, and Black Caribbean adults because these groups have higher health risks at lower BMI levels. Healthy weight for these groups is BMI 18.5–22.9 rather than 18.5–24.9.
What are the limitations of BMI calculation?
BMI doesn't account for muscle mass, bone density, or where fat is stored on your body. Athletes may have high BMI despite low body fat. Waist measurement and overall health context matter too. Always discuss your results with your GP for personalised health advice.
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.