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
What Is a BMI Check and Why Does the NHS Use It?
A BMI check measures your body weight in relation to your height using a simple formula, and it's one of the primary screening tools the NHS uses to assess whether your weight falls within a healthy range. The BMI formula divides your weight in kilograms by your height in metres squared. While BMI has limitations—it doesn't distinguish between muscle and fat, for example—the NHS considers it a useful starting point for identifying health risks related to excess weight. Understanding your BMI and how it compares to NHS guidelines can help you and your GP decide whether any weight management support or lifestyle changes might benefit your health.
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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 divides adults into five BMI categories, each with different health implications. A healthy BMI according to NHS guidance is between 18.5 and 24.9. If your BMI falls between 25.0 and 29.9, you're classified as overweight. A BMI of 30 or above is classified as obese, which the NHS further divides into three classes (I, II, and III) to reflect increasing health risk.
However, the NHS recognises that ethnicity affects health risk at different BMI levels. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage face higher risk of type 2 diabetes and heart disease at lower BMI thresholds. For these groups, the NHS recommends: healthy weight 18.5–22.9, overweight 23.0–27.4, and obese 27.5 and above. Use our free BMI calculator above to check where your weight falls within these NHS ranges instantly.
Your waist circumference also matters. The NHS recommends men keep their waist below 94cm (37 inches) and women below 80cm (31.5 inches) for optimal health.
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 Support
The NHS offers a structured approach to weight management across four tiers. Tier 1 includes self-help resources, digital tools, and community programmes. If you need more support, your GP can refer you to Tier 2 or Tier 3 specialist services, where you may receive behaviour change support, dietary advice, or prescription weight management medication. Tier 4 involves bariatric surgery for severe obesity with serious health complications.
You should speak to your GP if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess your individual health and discuss what support—whether lifestyle changes, referral to specialist services, or other options—might be right for you.
- 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 and how do I calculate my BMI?
The BMI formula divides your weight in kilograms by your height in metres squared (BMI = kg ÷ m²). For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73²) = 23.4. Use our free BMI calculator on this page to work this out instantly without doing the maths yourself.
Why does the NHS use different BMI thresholds for different ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage develop type 2 diabetes and heart disease at lower BMI levels than white European populations. The NHS adjusted thresholds for these groups to better reflect their actual health risk at each weight level. Your GP can advise which thresholds apply to you.
Is BMI a perfect measure of health?
No. BMI doesn't account for muscle mass, bone density, or where fat is stored on your body. Athletes may have a high BMI but low body fat. The NHS recommends considering BMI alongside waist circumference, fitness level, and overall health when assessing weight-related risks.
When should I contact my GP about my BMI?
Speak to your GP if your BMI is 30 or above, or 27–29.9 with health conditions like diabetes, high blood pressure, or sleep apnoea. Your GP can assess your individual health, discuss any concerns, and refer you to specialist weight management services if appropriate.
Can I convert between stone and kilograms to check my BMI?
Yes. Use our free weight converter on this page to switch between kg, stone, and pounds. Then use the BMI calculator to check your result against NHS healthy weight ranges. Converting accurately ensures your BMI calculation is correct.
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.