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 Calculate BMI for Adults — NHS Context
Calculating your BMI (Body Mass Index) is one of the most straightforward ways to understand whether your weight falls within a healthy range according to NHS guidelines. The BMI formula is simple: divide your weight in kilograms by your height in metres squared. For UK adults, the NHS uses standardised BMI categories to assess health risk, though it's important to understand that BMI has limitations and is just one screening tool. Your GP can provide personalised advice about what your BMI means for your individual health.
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 What They Mean
The NHS BMI categories for adults aged 18 and over are:
- Underweight: BMI below 18.5 — may indicate nutritional deficiency
- Healthy weight: BMI 18.5 to 24.9 — associated with lowest health risk
- Overweight: BMI 25.0 to 29.9 — increased risk of weight-related conditions
- Obese Class I: BMI 30.0 to 34.9 — significantly higher health risk
- Obese Class II: BMI 35.0 to 39.9 — substantially higher health risk
- Severely Obese: BMI 40.0+ — very high health risk
However, the NHS also recognises that ethnicity affects BMI interpretation. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage have higher health risks at lower BMI levels, so NICE recommends adjusted thresholds: healthy weight 18.5–22.9, overweight 23.0–27.4, and obese 27.5+. Use our free BMI calculator above to find your category 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 Support and When to Seek Help
The NHS offers a structured weight management pathway for adults. If your BMI falls outside the healthy range, your GP can assess whether you need support. The NHS typically recommends a tiered approach: start with self-help resources and digital tools (tier 1), move to primary care-based behaviour change programmes (tier 2), and access specialist weight management services for more intensive support (tier 3). For severe obesity with significant health complications, bariatric surgery may be considered (tier 4). NICE guidance emphasises that even a 5–clinically studied weight loss can improve blood pressure, blood sugar control, and reduce disease risk. Speak to your GP if you're concerned about your weight or health.
- 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 = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = BMI 22.9 (healthy weight). Use our BMI calculator above for gradual improvement.
What is a healthy BMI range according to the NHS?
For most UK adults, a healthy BMI is 18.5 to 24.9. However, for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower range: 18.5 to 22.9. Your GP can advise on the most appropriate range for you.
Why does the NHS have different BMI thresholds for different ethnicities?
Research shows that people from South Asian and Black African backgrounds develop weight-related health conditions like type 2 diabetes at lower BMI levels than other populations. Using adjusted thresholds ensures fairer health risk assessment across different ethnic groups.
What are the limitations of BMI?
BMI does not distinguish between muscle and fat — athletes may have a high BMI but low body fat. BMI also ignores where fat is stored (waist circumference matters). It's less accurate for elderly people and doesn't account for bone density or individual variation.
What should I do if my BMI indicates I'm overweight or obese?
Speak to your GP, who can assess your overall health and recommend appropriate support. The NHS offers weight management programmes, digital tools, and specialist services. Even small weight losses improve health. Use the weight converter on this page to track progress in your preferred units.
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.