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 Calculator and NHS Guidelines for UK Adults
A BMI calculator is a simple tool that uses your weight and height to assess whether you're in a healthy weight range according to NHS guidelines. BMI (Body Mass Index) is widely used by the NHS as a screening tool to identify health risks. However, it's important to understand what your BMI means, how the NHS uses it, and what limitations it has. Use our free BMI calculator above to check your personal BMI instantly, then read on to understand what your result means in NHS context.
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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 What They Mean
The NHS uses standardised BMI categories to classify whether an adult's weight falls into a healthy, overweight, or obese range. These BMI range UK thresholds apply to adults aged 18 and over:
- Below 18.5: Underweight — may indicate nutritional concerns
- 18.5–24.9: Healthy weight — associated with lowest health risk
- 25.0–29.9: Overweight — increased risk of weight-related health conditions
- 30.0–34.9: Obese (Class I) — significantly increased health risk
- 35.0–39.9: Obese (Class II) — high health risk
- 40.0+: Severely obese (Class III) — very high health risk
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: a healthy BMI range of 18.5–22.9, and overweight starting at 23.0. This is because these populations face higher cardiovascular and diabetes risks at lower BMI levels.
Clinically BackedWeight Loss
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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.
NHS Weight Management Support and When to See Your GP
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway. The NHS BMI calculator and guidance help your GP assess whether you need support. You should speak to your GP if you're concerned about your weight, especially if you have BMI limitations that complicate the picture — for example, if you're very muscular, pregnant, or have other health conditions. Your GP can refer you to tier 1 or tier 2 NHS weight management services, which provide behaviour change support, digital tools, and lifestyle programmes. For those with a BMI of 30 or above with weight-related health conditions, specialist tier 3 services may prescribe weight loss medication such as GLP-1 injections alongside lifestyle changes.
- 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 BMI formula?
BMI is calculated as weight (kg) divided by height in metres squared. For example, a person weighing 70kg and 1.73m tall has a BMI of approximately 23.4 (70 ÷ 1.73²). Our free BMI calculator above does this instantly — just enter your weight and height.
What is a healthy BMI according to the NHS?
The NHS defines a healthy BMI as 18.5–24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Caribbean heritage, the NHS recommends a slightly lower range of 18.5–22.9 due to higher health risks at similar BMI levels.
Why does the NHS use BMI if it has limitations?
BMI is a useful and quick screening tool at population level, but it doesn't distinguish between muscle and fat, doesn't account for age or frame size, and may be less accurate for athletes or elderly people. The NHS acknowledges these limitations and uses BMI alongside other measures like waist circumference and individual health assessment.
When should I see my GP about my BMI or weight?
Speak to your GP if you're concerned about your weight, have gained weight recently without explanation, have weight-related health symptoms (such as breathlessness or joint pain), or if your BMI falls outside the healthy range and you want support. Your GP can assess your individual health and refer you to NHS weight management services if appropriate.
Can I use a BMI calculator for children?
No — adult BMI categories do not apply to children. Children's BMI is assessed using age and sex-specific centile charts (the UK90 growth reference). Use the NHS Healthy Weight Calculator for children instead, or speak to your health visitor or GP for guidance on your child's healthy weight range.
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.