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 BMI Relates to Weight Loss — UK Guide
Your BMI (Body Mass Index) is a key starting point for understanding whether you're in a healthy weight range and what weight loss goal might be appropriate for you. This guide explains how the BMI formula works, what the NHS healthy weight ranges are, and how to use BMI to set realistic weight loss targets. Use our free BMI calculator above to find your personal BMI instantly, then read on to understand what it means for 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.
Understanding BMI Formula and NHS Categories
The BMI formula is straightforward: divide your weight in kilograms by your height in metres squared. For example, if you weigh 80kg and are 1.75m tall, your BMI would be approximately 26, which falls in the overweight category according to NHS guidelines.
The NHS BMI ranges for UK adults are:
- Below 18.5 — Underweight
- 18.5 to 24.9 — Healthy weight
- 25.0 to 29.9 — Overweight
- 30.0 to 34.9 — Obese (Class I)
- 35.0 to 39.9 — Obese (Class II)
- 40.0 and above — Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds, with healthy BMI starting at 18.5 and overweight beginning at 23.0.
To calculate your healthy weight range, multiply 18.5 and 24.9 by your height in metres squared. This gives you the kg range where you would have a healthy BMI. Use the weight converter on this page to see this in stone and pounds.
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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.
Using BMI to Set Weight Loss Goals
Once you know your BMI, you can work backwards to find a realistic weight loss target. If your BMI is above 25, aiming for the upper end of the healthy weight range (BMI 24.9) is a sensible first goal. The NHS recommends losing weight at a rate of 0.5 to 1kg per week for sustainable results — this usually requires a calorie deficit of around 500 calories per day.
Important: BMI has limitations. It does not distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite low body fat. Waist circumference is also important — men with a waist over 102cm and women over 88cm face higher health risks regardless of BMI. Your GP can provide personalised advice about your specific situation and whether weight loss medication or specialist support might be appropriate.
- 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 for weight loss?
A healthy BMI is between 18.5 and 24.9 according to NHS guidelines. If your BMI is above this range, losing weight to reach it can improve your health. However, even a 5–10% reduction in your current weight can bring meaningful health benefits. Use our BMI calculator above to find your target range.
How much weight should I lose based on my BMI?
The amount depends on your starting weight and height. To find your healthy weight range, multiply 18.5 and 24.9 by your height in metres squared. For example, at 1.70m tall, a healthy weight range is approximately 53–72kg (8st 4lbs to 11st 4lbs). Your GP can help you set a personalised target.
Does BMI tell the whole story about weight and health?
No. BMI does not account for muscle mass, where fat is stored, age, or ethnicity. Waist circumference is equally important — excess belly fat carries higher health risks. A high BMI combined with a large waist measurement suggests higher health risk. Always discuss your results with your GP.
Can I use a weight loss calculator with my BMI?
Yes. Our free GLP-1 weight loss calculator uses your BMI to estimate potential weight loss if you were to use prescription weight loss medication like Mounjaro or Wegovy. This can help you understand what realistic weight loss might look like alongside diet and exercise changes.
Are lower BMI thresholds used in the UK for certain ethnic groups?
Yes. The NHS recommends lower BMI thresholds for adults of South Asian, Chinese, Black African, and Black Caribbean heritage because these groups face higher risks of type 2 diabetes and heart disease at lower BMI levels. Healthy BMI for these groups starts at 18.5 and overweight begins at 23.0.
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.