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
NHS Body Mass Index — Understanding Your Score
Body Mass Index (BMI) is the standard measurement the NHS uses to assess whether your weight falls within a healthy range for your height. The NHS BMI calculator divides adults into categories based on their weight and height, helping you understand your personal health context. BMI is a quick screening tool, but it's important to know that it has limitations — it doesn't distinguish between muscle and fat, and healthy weight ranges vary based on your ethnicity. This guide explains how to interpret your NHS BMI score and what the categories mean for UK adults.
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.
How to Interpret Your NHS BMI Calculator Results
The NHS BMI categories for adults are straightforward: a healthy BMI sits between 18.5 and 24.9, an overweight BMI is 25.0 to 29.9, and obesity begins at 30.0. However, for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — a healthy BMI for these groups is 18.5 to 22.9, with overweight starting at 23.0. This difference exists because these populations face higher risks of type 2 diabetes and heart disease at lower BMI levels.
If your BMI falls outside the healthy range, use our free weight converter above to understand what your weight means in stone, lbs, or kg. Remember that BMI is a screening tool, not a diagnostic one. Your waist circumference also matters — the NHS notes that men with waist measurements over 94cm (37 inches) and women over 80cm (31.5 inches) have increased health risks even at a healthy BMI.
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.
BMI vs Body Composition — When Each Matters
BMI is useful for population-level health screening, but body composition — the ratio of fat to lean body mass — gives a more complete picture. Someone with high muscle mass might have a high BMI but low body fat percentage, which is healthier than the BMI alone suggests. Body fat percentage and lean body mass are better predictors of metabolic health for athletes or very muscular individuals. However, for most UK adults, BMI remains a reliable first-line assessment tool. Our free BMI calculator on this page will place you into the NHS categories instantly, and you can compare this with your waist circumference for a fuller understanding of your health risk profile.
- 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 according to the NHS?
A healthy BMI for most UK adults is 18.5 to 24.9. However, for South Asian, Chinese, Black African, and Black Caribbean adults, the NHS recommends a lower range of 18.5 to 22.9 because these groups face higher health risks at higher BMI levels. Use our free BMI calculator above to check your personal score.
Why does the NHS use different BMI thresholds for some ethnicities?
Research shows that South Asian, Chinese, Black African, and Black Caribbean populations develop type 2 diabetes and cardiovascular disease at lower BMI levels than other groups. The lower NHS thresholds for these communities reflect this increased metabolic risk, ensuring earlier intervention where needed.
Is BMI accurate for muscular people?
No. BMI doesn't distinguish between muscle and fat, so very muscular or athletic individuals may have a high BMI but low body fat percentage. In these cases, body composition measurements are more useful than BMI alone. Waist circumference is also a helpful additional measure.
What should I do if my BMI is outside the healthy range?
Start by speaking with your GP, who can assess your individual health and discuss options. The NHS recommends sustainable weight loss of 0.5 to 1kg per week through a balanced diet and physical activity. Our progress tracker can help you log and monitor your journey over time.
Can I use BMI if I'm pregnant or elderly?
BMI is less reliable during pregnancy and in elderly adults due to changes in body composition and fluid retention. If you're pregnant or over 65, ask your GP about personalised health assessments rather than relying on BMI alone.
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.