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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How to Figure Out Your BMI — NHS Guide
Understanding your BMI (Body Mass Index) is one of the first steps towards managing your health. The NHS uses BMI as a screening tool to assess whether your weight falls into a healthy range for your height. This guide explains the BMI formula, how to calculate it, and what your result means according to NHS guidelines. You can calculate your BMI instantly using our free BMI calculator above, or follow the simple formula yourself. Keep in mind that BMI has limitations—it doesn't account for muscle mass or where fat is stored—but it's a useful starting point for understanding your health.
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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 divides BMI results into clear categories to help you understand your weight status. These are the standard categories for most UK adults:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- Obese (Class I): BMI 30.0 to 34.9
- Obese (Class II): BMI 35.0 to 39.9
- Severely obese (Class III): BMI 40.0 and above
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends using lower BMI thresholds because these groups face higher health risks at lower weights. For these communities, a healthy BMI range starts at 18.5 and goes up to 22.9, with overweight beginning at 23.0. The NHS adjusts guidance to reflect this increased risk, so speak to your GP about what's appropriate for your background.
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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
If your BMI calculation shows you're overweight or obese, the NHS offers a structured approach to weight management across four tiers of support. Tier 1 includes self-help resources, digital tools, and community programmes—starting points you can access independently. Tier 2 involves your GP or practice nurse for behavioural support and monitoring. Tier 3 is specialist multidisciplinary weight management services, available through referral, where prescription weight loss medications may be considered. Tier 4 covers bariatric surgery for severe obesity. Use our free weight converter to track your weight in both kg and stone, and consider logging progress with our tracking tool. Your GP can assess which tier is right for you and discuss whether medical support would help.
- 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's the BMI formula and how do I calculate it myself?
The BMI formula is weight (kg) divided by height in metres squared. For example, if you weigh 70kg and are 1.75m tall, divide 70 by (1.75 × 1.75 = 3.06), which gives a BMI of approximately 23. You can use our free BMI calculator above to get an gradual improvement, or calculate it manually using this formula.
Why does the NHS have different BMI thresholds for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage develop weight-related health conditions like type 2 diabetes and heart disease at lower BMI levels than other groups. The NHS adjusts thresholds for these communities to provide earlier intervention and better health outcomes. Speak to your GP about which guidelines apply to you.
What does it mean if my BMI is in the healthy range but I'm still concerned about my weight?
BMI is a useful screening tool but has limitations—it doesn't distinguish between muscle and fat, and doesn't account for where fat is stored. You might have a healthy BMI but still benefit from improving fitness or diet. Your GP can assess your overall health, measure your waist circumference, and discuss any concerns beyond BMI.
Can I use the BMI calculator if I'm pregnant or elderly?
BMI is less accurate during pregnancy because it doesn't account for weight gain needed for the baby. Elderly adults may have lower muscle mass, making BMI less reliable. If you're pregnant or over 65, speak to your GP or midwife rather than relying on BMI alone. They can give you personalised guidance.
What should I do if my BMI shows I'm overweight—do I need to see my GP immediately?
Not urgently, but it's worth booking an appointment to discuss your overall health. Your GP can assess whether weight management support would help, discuss lifestyle changes, and rule out underlying health conditions affecting your weight. The NHS offers support at every stage, starting with self-help resources and progressing to specialist care if needed.
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.