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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Age to Weight Scale — Understanding Healthy Weight Across Life Stages
There is no single "correct" weight for a given age — healthy weight depends on height, body composition, and individual health factors rather than age alone. However, age does influence metabolism, muscle mass, and health considerations around weight management. The NHS uses BMI (Body Mass Index) as the primary screening tool regardless of age, with the same healthy weight range (BMI 18.5–24.9) applying to all adults. This guide explains how age relates to weight, what healthy weight means across different life stages, and how to use our free weight converter and BMI calculator to find your personal healthy weight range.
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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
As you age, several physiological changes affect weight management. Metabolism naturally slows with age — you burn approximately 3–8% fewer calories per decade after age 30, primarily because muscle mass declines (sarcopenia). This means maintaining the same weight requires fewer calories as you get older, and weight gain becomes easier unless activity levels increase or calorie intake adjusts.
However, healthy weight ranges remain constant across adulthood. The NHS recommends the same BMI categories (18.5–24.9 for healthy weight) for all adults aged 18–65, regardless of age. For adults over 65, some clinical guidance suggests slightly higher BMI thresholds may be acceptable (BMI 24–29 can be appropriate), as very low BMI in older adults is associated with muscle loss and frailty risk.
- 20s–40s: Peak muscle mass and metabolism — weight gain typically reflects lifestyle changes
- 40s–60s: Gradual metabolic slowdown and muscle loss — weight management requires attention to activity and diet
- 60+: Significant muscle loss accelerates — maintaining healthy weight protects bone density and mobility
Use our free BMI calculator above to find your personal healthy weight range based on your height, regardless of your 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.
Healthy Weight Ranges — What the NHS Says
The NHS uses BMI (weight in kg ÷ height in metres²) to define healthy weight. A BMI between 18.5 and 24.9 is considered healthy for all adults. You can instantly convert your weight using our free weight converter and check your BMI with our calculator on this page.
For South Asian, Chinese, Black African, and Black Caribbean adults: The NHS recommends lower BMI thresholds because these groups face higher cardiovascular and diabetes risk at the same BMI. Healthy weight is 18.5–22.9 for these populations.
Weight is just one health marker. Waist circumference, fitness level, blood pressure, and blood sugar control also matter. Your GP can assess what healthy weight means for you personally, considering your individual health conditions and family history. Sustainable weight management combines balanced nutrition, regular physical activity, and realistic, gradual changes — not gradual weight management.
- 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 with age?
Healthy BMI ranges (18.5–24.9) remain the same across adulthood aged 18–65. However, metabolism slows with age, making weight management more challenging. For adults over 65, slightly higher BMI (24–29) may be clinically appropriate to preserve muscle mass. Your GP can advise on healthy weight for your individual circumstances.
Why is metabolism slower in older age?
Muscle mass naturally declines with age (sarcopenia) — you lose approximately 3–8% of muscle per decade after 30. Muscle burns more calories at rest than fat, so reduced muscle means lower daily calorie burn. Regular strength training and adequate protein can help maintain muscle mass and metabolism as you age.
What is a healthy weight for a 50-year-old woman?
Healthy weight depends on height, not age. Use the BMI calculator on this page — enter your height and target a BMI of 18.5–24.9 (or 18.5–22.9 if you're South Asian, Chinese, Black African, or Caribbean). Your GP can discuss your personal healthy weight range considering your health history.
Can I use a weight-for-age chart like a child's growth chart?
No — adult weight-for-age charts are not clinically valid. Children use age and sex-specific growth charts; adults use BMI regardless of age. The NHS recommends BMI as the screening tool for all adults. Individual healthy weight varies widely based on height and body composition, not age.
How can I track weight changes over time?
Use our free progress tracker on this site to log your weight, track trends, and monitor your journey. Combine this with regular activity, balanced eating, and support from your GP. Small, sustainable changes (0.5–1 kg per week) are more likely to last than gradual weight management.
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.