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 Height, Weight, and Age Affect Your Health
Your height, weight, and age are three key factors that determine your overall health status and weight management needs. In the UK, the NHS uses these measurements together to assess whether your weight is healthy and to identify any increased health risks. Age affects metabolism, muscle mass, and how your body stores weight — which means your ideal weight range may change over time. Understanding how these three factors work together helps you make informed decisions about your health and when to seek advice from your GP.
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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.
How BMI Changes With Height, Weight, and Age
BMI (Body Mass Index) is calculated using your weight and height only — it does not account for age directly. However, age significantly affects how your body composition changes. As you age, you naturally lose muscle mass and may gain fat, even if your weight stays the same. This means two people of identical height and weight but different ages may have different health risks.
Using our free BMI calculator above, you can check your personal BMI instantly. The NHS categorises BMI as follows:
- Under 18.5 = Underweight
- 18.5 to 24.9 = Healthy weight
- 25.0 to 29.9 = Overweight
- 30.0 and above = Obese
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply — a healthy BMI starts at 18.5 but the overweight threshold begins at 23.0 instead of 25.0. Age does not change these thresholds, but it does affect how quickly you may develop weight-related health conditions. Younger adults with high BMI may not yet show symptoms, whilst older adults at the same BMI may already experience joint problems, high blood pressure, or type 2 diabetes.
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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.
Healthy Weight Ranges Across Different Ages
A healthy weight range depends on your height, not your age — but your age affects your metabolic rate and how easily you maintain that weight. Younger adults typically have faster metabolisms, whilst older adults may need to adjust their diet and activity levels to maintain the same weight.
To find your healthy weight range for your height, use our free BMI calculator and weight converter above. For example, an adult 5ft 8in (173cm) tall has a healthy weight range of approximately 55kg to 74kg (8st 8lbs to 11st 8lbs). This range applies equally to a 25-year-old and a 65-year-old — but the 65-year-old may find it requires more deliberate physical activity and careful nutrition to achieve and maintain. Your GP can discuss your individual healthy weight target and whether any weight management support would benefit 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.
Does age affect what weight is healthy for me?
Age does not change BMI categories — a healthy BMI range is 18.5 to 24.9 for all adults regardless of age. However, age affects metabolism, muscle mass, and how quickly weight-related health conditions develop. Older adults at a higher BMI may experience health problems sooner than younger adults at the same BMI. Your GP can assess your personal health risk based on your age, weight, and other factors.
How does metabolism change with age?
Metabolism naturally slows by approximately 2–8% per decade after age 30, primarily due to loss of muscle mass. This means you may need fewer calories to maintain the same weight as you age. Staying physically active, particularly with strength training, helps preserve muscle mass and keep metabolism higher as you get older.
Can I use the same healthy weight range my whole life?
Your healthy weight range based on height remains the same throughout your life — a BMI of 18.5 to 24.9 applies from young adulthood through older age. However, achieving and maintaining that weight may require different strategies at different life stages. Hormonal changes (menopause in women, testosterone decline in men) can affect weight distribution. Your GP can advise on age-appropriate weight management.
Should I aim for a different weight if I'm over 65?
The NHS BMI categories do not change for older adults — a healthy BMI remains 18.5 to 24.9 regardless of age. Some research suggests slightly higher BMI in older adults may be associated with better outcomes, but this remains debated. Your GP can discuss the best weight range for your individual health, fitness level, and medical conditions.
How can I use my height, weight, and age to check my health?
Calculate your BMI using your height and weight with our free BMI calculator above. Compare your BMI to NHS categories. Then discuss the result with your GP, mentioning your age, lifestyle, and any weight-related health concerns. Your GP may also consider your waist measurement, blood pressure, and other health markers alongside your BMI and age.
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.