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 To Measure Your BMI — NHS Context
Measuring your BMI is straightforward using a simple formula based on your height and weight. The NHS uses BMI as a screening tool to assess whether you're at a healthy weight, though it's important to understand both how it works and its limitations. This guide explains the BMI formula, NHS categories, and what happens next if you want personalised health advice. You can also use our free BMI calculator above to work out your result instantly.
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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.
NHS BMI Formula and Categories
The BMI formula is simple: divide your weight in kilograms by your height in metres squared (BMI = weight ÷ height²). For example, if you weigh 70kg and are 1.75m tall, your BMI is 22.9, which falls in the healthy weight range.
The NHS uses these standard BMI categories for UK adults:
- Below 18.5 — Underweight
- 18.5 to 24.9 — Healthy weight
- 25.0 to 29.9 — Overweight
- 30.0 to 34.9 — Obese (Class I)
- 35.0 to 39.9 — Obese (Class II)
- 40.0 and above — Severely obese (Class III)
However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these groups face higher health risks at lower BMI levels. For these groups, the healthy range is 18.5 to 22.9, and overweight begins at 23.0.
Try our BMI calculator on this page to find your category instantly, or use our weight converter to adjust your measurements between kg, stone, and pounds.
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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 and Next Steps
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway to support you. Tier 1 starts with self-help resources and lifestyle advice through your GP or local community programmes. If you need more support, your GP can refer you to Tier 2 or Tier 3 specialist services, where you may be offered structured weight loss programmes, behaviour change support, or prescription medication alongside dietary and physical activity guidance.
Remember that BMI is a screening tool, not a diagnosis — it doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a higher BMI without excess body fat. Your GP can assess your individual health context and discuss whether further action is needed.
- 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 if I use stone and pounds?
Convert to kilograms first (1 stone = 6.35 kg), then use the formula: weight (kg) ÷ height (m)². Alternatively, use our free weight converter above to switch between stone, pounds, and kilograms instantly.
What is a healthy BMI according to the NHS?
The NHS defines healthy BMI as 18.5 to 24.9 for most UK adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9 due to higher health risk at lower weights.
Does BMI account for muscle mass?
No — BMI doesn't distinguish between muscle and fat. Athletes, very fit individuals, and people with high muscle mass may have a higher BMI without excess body fat. Your GP can discuss whether your BMI accurately reflects your health.
What should I do if my BMI is above the healthy range?
Start with your GP, who can discuss your individual health context and offer support. The NHS offers free weight management resources at Tier 1, and if you need specialist help, your GP can refer you to Tier 2 or Tier 3 services for additional guidance.
Why are BMI thresholds lower for South Asian and Black African populations?
Research shows these groups face higher risks of type 2 diabetes and cardiovascular disease at lower BMI levels. The NHS recommends lower thresholds (healthy range 18.5–22.9) to identify health risk earlier in these populations.
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.