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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BMI Percentile Calculator — NHS Health Context
A BMI percentile calculator helps you understand where your weight sits within NHS health guidelines and population ranges. Unlike raw BMI numbers, percentiles show how your BMI compares to others of the same age and sex. This page explains NHS BMI categories, how to use the BMI formula to calculate your own percentile, and what the NHS recommends when your BMI falls outside the healthy range. Use our free BMI calculator above to find your personal BMI and get NHS-aligned guidance instantly.
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 Healthy Weight Ranges
The NHS defines healthy BMI as between 18.5 and 24.9 kg/m². These categories apply to most UK adults:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Obese (Class II): BMI 35.0–39.9
- Severely obese: BMI 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher cardiovascular and metabolic risks at the same BMI. For these populations, a healthy BMI range starts at 18.5 and extends to 22.9. The overweight threshold begins at 23.0 instead of 25.0. Important: BMI is a screening tool only—it does not account for muscle mass, bone density, or where fat is stored. Your GP can provide personalised interpretation of your individual BMI result and overall health context.
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 Pathway and When to Seek Help
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway. Tier 1 includes self-help resources and digital tools like our free BMI calculator and progress tracker. Tier 2 involves your GP, who may recommend behaviour change support or refer you to specialist services. Tier 3 provides access to specialist multidisciplinary weight management services, where prescription medications such as GLP-1 injections may be considered. Tier 4 is reserved for bariatric surgery in cases of severe obesity with significant health complications. Many GP practices offer free weight management support—contact yours to discuss your individual situation. Early intervention at lower BMI levels often produces better long-term outcomes.
- 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 NHS guidelines?
The NHS defines a healthy BMI as between 18.5 and 24.9 kg/m² for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5–22.9 because these groups have higher health risks at higher BMI levels. Use our free BMI calculator to check your personal result instantly.
How do I calculate my BMI using the BMI formula?
The BMI formula is: weight (kg) divided by height (metres) squared. For example, if you weigh 70kg and are 1.75m tall, your BMI = 70 ÷ (1.75 × 1.75) = 22.86. Our BMI calculator on this page does this automatically—just enter your weight and height in UK measurements.
What should I do if my BMI is outside the healthy range?
Contact your GP, who can assess your individual health and discuss next steps. The NHS offers a structured pathway from self-help resources (Tier 1) through to specialist weight management services (Tier 3) and surgery (Tier 4). Your GP can determine which tier is appropriate for you.
Why does BMI differ by ethnicity in NHS guidance?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage face higher risks of type 2 diabetes and heart disease at lower BMI levels than other populations. The NHS therefore recommends lower BMI thresholds for these groups to identify health risks earlier and enable preventive intervention.
What are the limitations of BMI as a health measure?
BMI does not distinguish between muscle and fat, so athletes may have high BMI despite low body fat. It also does not account for where fat is stored (belly fat carries higher risk), age-related muscle loss, or pregnancy. Use BMI alongside other measures like waist circumference and discuss results with your GP for full health context.
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.