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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What's Your Optimal Weight By Height and Age?
Your optimal weight depends on your height, age, and body composition — not just a single number. The NHS uses BMI (body mass index) as the primary screening tool to assess healthy weight ranges, though this varies by ethnicity and age. In this guide, we'll show you how to find your personal healthy weight range, explain the factors that influence it, and help you understand what healthy weight means for your individual health. Use our free BMI calculator to check where you stand right now.
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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.
How to Calculate Your Healthy Weight Range
Your healthy weight range is based on your height and BMI (body mass index), a measure of body fat based on height and weight. The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. To find your range, multiply your height in metres squared by 18.5 (lower bound) and 24.9 (upper bound).
Example: For someone 1.73m tall (5ft 8in):
- Lower healthy weight: 18.5 × (1.73)² = 55.4 kg (8st 10lbs)
- Upper healthy weight: 24.9 × (1.73)² = 74.5 kg (11st 10lbs)
However, ethnicity matters: For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: 18.5 to 22.9. This is because these groups face higher health risks from type 2 diabetes and cardiovascular disease at lower BMI levels. Our free weight converter and BMI calculator make this simple — enter your height and current weight to see your personal BMI and healthy range instantly.
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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.
Why Age and Other Factors Matter
Age itself doesn't change your BMI calculation, but it does affect health context. Muscle naturally decreases with age, so two people of the same BMI may have different body composition. A 25-year-old at BMI 25 may be relatively lean, whilst a 65-year-old at the same BMI may have higher body fat percentage due to lost muscle mass.
Other factors influencing your optimal weight include:
- Genetics — family history influences metabolic rate and fat distribution
- Medical conditions — hormonal disorders, medications, and health issues affect weight
- Physical activity level — muscle weighs more than fat, so active individuals may weigh more at a healthy BMI
- Body frame size — larger frames may naturally weigh more within a healthy range
For personalised guidance tailored to your age and health history, speak to your GP. They can assess whether your current weight poses any health risks and suggest a realistic target based on your individual circumstances.
- 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 difference between healthy weight and ideal weight?
Healthy weight is a range (based on BMI) where the majority of adults have lower health risks. Ideal weight is more individual — it accounts for muscle, bone density, age, and genetics. Your healthy BMI range is a useful starting point, but your ideal weight within that range depends on your personal health and fitness goals. Our BMI calculator shows both your current BMI and your healthy range for your height.
Does optimal weight change as you get older?
Your BMI calculation doesn't change with age, but research suggests slightly higher BMI may be associated with better outcomes in older adults (65+). However, this is still being studied. The main change with age is body composition — muscle decreases naturally, so weight loss with age often requires more physical activity to maintain muscle. Your GP can advise on realistic targets for your age and health status.
Why do men and women have different average weights at the same height?
Women typically have less muscle mass and higher body fat percentage than men at the same height and BMI, due to biological differences in muscle distribution and hormonal factors. However, the BMI formula is the same for both — healthy BMI ranges don't differ by sex. Both sexes use the same 18.5 to 24.9 healthy range (or 18.5 to 22.9 for certain ethnicities).
Is BMI the only measure of healthy weight?
No. BMI is a useful screening tool, but it doesn't account for muscle mass, body fat distribution, or where fat is stored. Waist circumference is also important — increased abdominal fat carries higher health risks. Men should aim for under 94cm (37in), women under 80cm (31.5in). For a fuller picture of your health, combine BMI with waist measurement and discuss with your GP.
How can I find my optimal weight if I'm recovering from weight loss treatment?
If you've used weight loss medication (like GLP-1 injections) or other weight management strategies, your optimal weight is whatever feels sustainable long-term whilst maintaining good health. Try our free progress tracker to log your weight and see trends over time. Continue using our weight converter and BMI calculator regularly to monitor your progress, and work with your GP to establish a realistic maintenance target based on how you feel and your health markers.
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.