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
Understanding BMI Levels — NHS Categories Explained
BMI levels are used by the NHS to assess whether your weight is in a healthy range for your height. The BMI formula divides your weight in kilograms by your height in metres squared. The NHS classifies BMI into five main categories — underweight, healthy weight, overweight, obese, and severely obese — each with different health implications. Understanding where your BMI falls helps you identify whether lifestyle changes or professional support might be beneficial. This guide explains NHS BMI categories and what they mean for your health in the UK context.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Thresholds
According to NHS guidance, BMI levels are classified as follows:
- Below 18.5 — Underweight
- 18.5 to 24.9 — Healthy weight (normal range)
- 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)
For most UK adults, a healthy BMI range sits between 18.5 and 24.9. However, the NHS recognises that ethnicity affects health risk at the same BMI. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage have lower recommended thresholds — a healthy BMI for these groups is 18.5 to 22.9, and the overweight threshold begins at 23.0. This reflects evidence showing these populations face higher risks of type 2 diabetes and heart disease at lower BMI levels. Our free BMI calculator above can help you determine your personal BMI instantly.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 When to Seek Help
The NHS recommends seeking support if your BMI falls outside the healthy range, particularly if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess your individual health and may refer you to a tier 3 specialist weight management service if appropriate. The NHS weight management pathway includes self-help resources, community programmes, prescription medications (in specialist services), and bariatric surgery for severe cases. Early action is most effective — losing just 5–10% of your body weight can significantly improve health outcomes. Use our weight converter to understand your weight in different units, and remember that BMI limitations exist: it doesn't account for muscle mass or fat distribution, so your GP may discuss additional measures like waist circumference.
- 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 healthy BMI level according to the NHS?
The NHS defines a healthy BMI as 18.5 to 24.9 for most adults. However, for South Asian, Chinese, Black African, and Black Caribbean adults, the healthy range is 18.5 to 22.9 due to higher health risks at lower BMI levels. Your GP can advise on what's healthy for you personally.
Is BMI the only measure of weight health?
No. While BMI is a useful screening tool, it has limitations — it doesn't distinguish between muscle and fat, and doesn't account for where fat is stored. The NHS also considers waist circumference (over 94cm for men or 80cm for women indicates increased health risk) and overall health history when assessing weight.
What should I do if my BMI is in the overweight range?
If your BMI is 25–29.9, the NHS recommends lifestyle changes including a balanced diet and regular physical activity. If you have weight-related health conditions, speak to your GP about further support. The NHS Weight Loss Plan and community programmes can help, or you may be referred to specialist services.
When does the NHS offer prescription weight loss medication?
The NHS offers prescription weight loss medication through specialist tier 3 weight management services, typically for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Access varies by region. Your GP can discuss referral if appropriate.
Does BMI level differ for children?
Yes. Children's BMI uses age and sex-specific centile charts, not adult categories. The NHS uses the UK90 growth reference charts. If you're concerned about a child's weight, speak to your health visitor or GP rather than using adult BMI categories.
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.