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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Weight and Height With Age in the UK
Your weight and height remain relatively stable in adulthood, but health risk profiles change with age. The NHS recognises that the same BMI can have different health implications depending on whether you're in your 30s, 50s, or 70s. This UK health guide explains how age affects weight management, what healthy weight ranges look like across different life stages, and when to seek GP advice about weight-related health changes. Use our free BMI calculator to check your current health status regardless of age.
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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 Weight Changes Across UK Adult Life Stages
In the UK, healthy weight ranges remain consistent by BMI category (18.5–24.9 kg/m²) across adulthood, but age significantly affects how your body handles weight and metabolism. In your 20s–40s, weight gain is often driven by lifestyle factors. By your 50s–60s, hormonal changes—particularly menopause in women—can shift where your body stores fat, even without weight increase. After 70, muscle loss becomes more pronounced, which can mask actual health risks even if weight appears stable.
- Ages 20–40: Metabolic rate is highest; weight gain usually reflects calorie imbalance or reduced activity
- Ages 40–60: Metabolism slows by approximately 5% per decade; hormonal changes increase abdominal fat storage
- Ages 60+: Muscle loss accelerates; same weight may indicate higher body fat percentage than in younger adults
The NHS emphasises that managing weight throughout these stages through balanced diet and physical activity reduces risk of type 2 diabetes, cardiovascular disease, and joint problems. Our free weight converter helps you understand your weight in UK measurements (stone and pounds) relevant to your health status at any age.
Clinically BackedWeight Loss
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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.
UK Guidance: Weight Management and Healthy Weight by Age
NHS guidance does not use age-specific BMI thresholds for adults—a BMI of 25–29.9 is "overweight" and 30+ is "obese" regardless of age. However, the British Medical Association and NICE recommend that GPs consider muscle mass, bone density, and individual health conditions when interpreting BMI in older adults. For South Asian, Chinese, Black African, and Black Caribbean adults of any age, lower BMI thresholds apply (healthy range 18.5–22.9). Use our BMI calculator above to find your personal BMI, then discuss the results with your GP, who can assess whether your weight is appropriate for your individual health profile, age, and medical history. Weight management at any age is most effective alongside increased physical activity and balanced nutrition.
- 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 healthy weight change as you get older in the UK?
No—NHS healthy weight BMI ranges (18.5–24.9) are the same at any age. However, body composition changes with age: older adults may have higher body fat at the same weight due to muscle loss. Your GP can assess whether your weight is healthy for your individual circumstances, regardless of age.
Why do people gain weight with age?
Metabolism slows by approximately 5% per decade after age 30. Physical activity often decreases. Hormonal changes, particularly menopause in women, increase abdominal fat storage. Medication side effects and medical conditions also contribute. Weight gain is not inevitable—many adults maintain stable weight through consistent diet and activity.
Is BMI accurate for older adults?
BMI is less accurate for older adults because it does not account for muscle loss. An older adult at BMI 28 may have higher actual body fat than a younger adult at BMI 28. Waist circumference is also important: men over 102cm and women over 88cm face increased health risk. Discuss your personal BMI with your GP for context.
What weight management support is available on the NHS in the UK?
The NHS offers Tier 1 support (self-help, digital tools, community programmes), Tier 2 primary care behaviour change support, and Tier 3 specialist multidisciplinary weight management services. Access varies by region. Referral to specialist services typically comes from your GP and may include prescription weight loss support for eligible adults.
Should I follow different diets at different ages?
General principles—balanced nutrition, adequate protein, regular physical activity—apply at all ages. Older adults should ensure sufficient protein to protect muscle mass. Younger adults may benefit from establishing healthy habits early. A GP or registered dietitian can advise on age-appropriate, personalised nutrition. Our weight loss calculator can help estimate potential outcomes with lifestyle changes or prescribed medication.
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.