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 Should Your BMI Be?
Your BMI (body mass index) should ideally fall between 18.5 and 24.9 according to NHS guidelines — this is considered a healthy weight range for most UK adults. However, the target BMI for you depends on your height, weight, age, ethnicity, and overall health. BMI is a useful screening tool, but it's just one measure of health. Use our free BMI calculator above to find out where you currently fall, and discover what a healthy BMI means for your individual circumstances.
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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 Healthy Ranges
The NHS BMI categories divide adults into four main groups based on their BMI formula result (weight in kg divided by height in metres squared):
- Underweight: Below 18.5 — may indicate insufficient nutrition or underlying health issues
- Healthy weight: 18.5–24.9 — the healthy BMI range recommended by NHS guidelines
- Overweight: 25.0–29.9 — increased health risks including type 2 diabetes and heart disease
- Obese Class I: 30.0–34.9 — significantly elevated health risks
- Obese Class II: 35.0–39.9 — high risk of serious health complications
- Severely obese: 40.0+ — very high risk requiring medical intervention
However, if you are of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI range thresholds are lower: healthy weight is 18.5–22.9, and overweight begins at 23.0. This reflects higher cardiovascular and diabetes risk in these populations at standard BMI levels.
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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, it has significant limitations. BMI limitations include: it cannot distinguish between muscle and fat (athletes may have high BMI but low body fat), it ignores where fat is stored on your body, and it doesn't account for age, bone density, or hormonal changes. The overweight BMI threshold of 25.0 may not reflect your true health risk. Instead of relying on BMI alone, your GP may also assess your waist circumference (over 94cm for men or 80cm for women indicates increased risk). Use our weight converter above to check your weight in different units, then discuss your personal BMI target with your GP or healthcare professional — they can assess your individual health picture and advise whether your current weight poses any health risks.
- 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 a normal BMI for an adult in the UK?
According to NHS guidelines, a normal (healthy) BMI for UK adults is between 18.5 and 24.9. However, for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is narrower: 18.5–22.9. Your ideal BMI depends on your individual height, weight, and health factors — consult your GP for personalised advice.
Is a BMI of 25 overweight?
Yes, according to NHS classifications, a BMI of 25.0–29.9 is considered overweight. This range indicates increased health risks compared to a healthy BMI, but it does not automatically mean you require treatment. Your GP can assess your overall health, waist measurement, and medical history to determine if weight management is appropriate for you.
What BMI should I aim for?
Most UK adults should aim for a BMI of 18.5–24.9 (healthy weight range). However, your personal target depends on your height, age, ethnicity, fitness level, and any underlying health conditions. Rather than aiming for a specific BMI number, focus on achieving a weight at which you feel healthy and energetic. Your GP can help set a realistic, personalised target.
How do I calculate my BMI?
BMI = weight (kg) ÷ height (metres)². For example, if you weigh 70kg and are 1.73m tall: 70 ÷ (1.73 × 1.73) = 23.4 BMI. Our free BMI calculator above does this instantly — simply enter your weight and height to see your result and which NHS category you fall into.
Why are BMI thresholds different for different ethnicities?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher risks of type 2 diabetes and heart disease at lower BMI levels than white European populations. The NHS therefore recommends lower BMI thresholds for these groups: healthy weight 18.5–22.9 instead of 18.5–24.9. This reflects genetic and metabolic differences, not differences in health importance.
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.