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
Free tracker included with every download this week
Age of Weight — Understanding Weight Changes Across Life Stages
As you age, your body composition and metabolism naturally change, which affects how your weight is managed and what a healthy weight means for you. In the UK, the NHS recognises that weight management strategies should be tailored to age, as factors like muscle loss, hormonal changes, and metabolic rate all shift throughout life. Understanding how age influences your weight helps you set realistic health goals and access appropriate support 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 Age Affects Weight and Metabolism in the UK
Metabolic rate declines with age. From around age 30, most adults lose approximately 3–8% of muscle mass per decade, which slows metabolism and makes weight gain more likely even without dietary changes. This is called sarcopenia. Additionally, hormonal shifts — including reduced oestrogen in women during menopause and lower testosterone in men — increase fat storage, particularly around the abdomen.
- Young adults (18–30): Higher metabolic rate, muscle mass peaks, weight changes often linked to lifestyle choices
- Middle-aged adults (30–50): Metabolism slows, hormonal changes begin, weight management requires more intentional effort
- Older adults (50+): Greater muscle loss, reduced activity levels, weight loss becomes harder but remains important for health
The NHS emphasises that healthy weight management at any age requires a combination of balanced nutrition, physical activity, and realistic expectations. Our free BMI calculator accounts for your current measurements, giving you context for your age group, though your GP can provide personalised guidance on what healthy weight means specifically for you.
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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.
Weight Management Strategies Across Different Ages
Younger adults often benefit from building healthy habits early — regular exercise and balanced nutrition establish foundations that pay dividends later. Middle-aged and older adults benefit from strength training to preserve muscle, consistent cardio activity, and increased protein intake. The NHS recommends at least 150 minutes of moderate aerobic activity weekly for all adults, with added strength work 2+ days per week.
Weight loss, when needed, should be gradual — the NHS advises 0.5–1 kg per week for sustainable results. Older adults should work with their GP before starting any weight loss programme, especially if managing existing health conditions. Use our free weight converter and progress tracker to monitor your journey in measurements that feel natural to you (stone, kg, or lbs), and remember that healthy weight at 25 looks different from healthy weight at 65.
- 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 metabolism really slow down with age?
Yes. Most adults experience a 2–8% metabolic decline 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. Regular strength training and adequate protein intake help slow this process.
What is a healthy weight for my age?
Healthy weight is based on BMI (18.5–24.9), not age directly. However, what constitutes a healthy weight range for your height stays the same across adulthood. Use our BMI calculator above to check your personal range, then discuss context with your GP, as individual factors matter.
Is it harder to lose weight as you get older?
Yes, typically. Slower metabolism, hormonal changes, and reduced muscle mass make weight loss harder, but it remains achievable and important for health. Older adults may see slower results but benefit from the same principles: calorie deficit, strength training, and consistency.
Should older adults aim for gradual weight management?
No. The NHS recommends all adults, including older adults, lose weight gradually at 0.5–1 kg per week. Rapid loss increases risk of muscle loss, nutritional deficiency, and gallstones. Slower, sustainable loss is healthier and more maintainable long-term.
Can prescription weight loss treatments work for older adults?
Some older adults may be eligible for prescription weight management support through their GP or NHS specialist services, depending on individual health factors and BMI. Age alone is not a barrier, but your GP will assess suitability based on your complete health profile and any existing medications.
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.