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
How to Test Your BMI — NHS Health Guidance
Testing your BMI (body mass index) is one of the first steps to understanding your weight and health. The BMI formula is straightforward: divide your weight in kilograms by your height in metres squared. The NHS uses BMI as a screening tool to assess whether you're in a healthy weight range, and the calculation works the same for all adults. Our free BMI calculator above does this instantly, but understanding how it works helps you interpret your result in the context of NHS health guidance and what it means for you personally.
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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 Your Result Means
The NHS BMI formula is: weight (kg) ÷ height (m)². Once you have your BMI number, the healthy BMI range according to NHS guidelines is 18.5 to 24.9. The main BMI categories UK adults fall into are:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight
- 25.0–29.9: Overweight
- 30.0–34.9: Obese (Class I)
- 35.0–39.9: Obese (Class II)
- 40.0+: Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the overweight BMI threshold is lower — the healthy range starts at 18.5 but overweight begins at BMI 23.0. This is because these groups face higher cardiovascular and metabolic disease risk at lower BMI levels. Use our free BMI calculator to check your personal result instantly, and cross-reference it with these NHS categories.
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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 Pathway and When to Seek Help
If your BMI limitations concern you — remember, BMI doesn't account for muscle mass or where fat is stored — your GP can offer a fuller health assessment. The NHS has a structured weight management pathway: Tier 1 involves self-help and digital tools (like our calculator), Tier 2 is primary care support, and Tier 3 is referral to specialist weight management services where prescription medications may be offered. If your BMI falls outside the healthy range, or if you have weight-related health concerns like high blood pressure or prediabetes, book an appointment with your GP. They can assess your individual situation and discuss whether you'd benefit from lifestyle changes, weight management support, or other interventions tailored to your health needs.
- 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's the exact NHS BMI formula?
The formula is weight (kg) ÷ height (metres)². For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73)² = 23.4. This falls in the healthy weight range according to NHS guidelines. You can calculate this instantly using our BMI calculator above.
Is a BMI of 25 overweight according to NHS?
Yes, according to NHS guidelines, a BMI of 25.0–29.9 is classified as overweight. A BMI of 25 is at the lower end of the overweight range. If you're in this range and have weight-related health conditions like high blood pressure, your GP may recommend lifestyle changes or further assessment.
Why are BMI thresholds different for South Asian adults?
The NHS recommends lower BMI thresholds for South Asian, Chinese, Black African, and Black Caribbean adults because research shows these groups have higher risks of type 2 diabetes and heart disease at lower BMI levels. For these populations, overweight starts at BMI 23.0 rather than 25.0.
What's the difference between BMI limitations and BMI usefulness?
BMI is a useful screening tool but doesn't distinguish between muscle and fat, and ignores where fat is stored. A muscular athlete may have a high BMI despite low body fat. For a complete picture, your GP may also measure waist circumference and assess other health markers alongside BMI.
Should I see my GP if my BMI is 26?
A BMI of 26 is in the overweight range. If you're otherwise healthy with no weight-related conditions, you might focus on lifestyle changes. However, if you have comorbidities like prediabetes or high blood pressure, or if you'd like professional guidance, your GP can offer personalised advice and may refer you to NHS weight management support services.
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.