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
How Does Weight Change With Age?
Weight naturally changes throughout life, and understanding what's normal at different ages helps you stay healthy. In the UK, NHS guidance recognises that weight management varies across life stages — from young adults to older age. Factors like metabolism, muscle mass, hormones, and activity levels all shift with age. This guide explains how weight changes across the lifespan and what healthy weight management looks like at each stage, using NHS health information and UK health data.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Weight Changes Across Life Stages — NHS Guidance
Young adults (18–30 years): Metabolism is typically highest in this age group. Many young adults reach their peak weight around the late 20s. This is a good time to establish healthy eating and activity habits that support long-term health.
Middle-aged adults (30–50 years): Metabolism gradually slows by approximately 2–8% per decade. Many people gain 0.5–1 kg per year during this stage, particularly around the abdomen. Hormonal changes (especially in women approaching menopause) can increase weight gain. Regular physical activity becomes increasingly important to maintain muscle mass and bone density.
Older adults (50+ years): Muscle mass naturally declines (sarcopenia) at a rate of 3–8% per decade after age 30. This reduces resting metabolic rate and increases the risk of weight gain if calorie intake isn't adjusted. However, maintaining a healthy BMI remains important for preventing heart disease, type 2 diabetes, and mobility problems. NHS guidance emphasises that healthy weight management at any age reduces these health risks.
Use our free BMI calculator above to check whether your current weight falls within a healthy range for your height, regardless of your age.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Managing Weight as You Age — Practical Steps
The key to managing weight across life stages is adapting your approach to your changing body. Strength training becomes increasingly important with age to preserve muscle mass — aim for resistance exercise at least twice weekly. Protein intake should remain adequate (1.0–1.2g per kg bodyweight for older adults) to support muscle maintenance. Regular physical activity, even walking, helps maintain metabolism and reduces disease risk. Most importantly, speak to your GP if your weight changes significantly or if you have concerns about your health. Your GP can assess your individual circumstances, consider any medical conditions affecting weight, and recommend personalised nutrition and exercise guidance tailored to your age and health status.
- 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 weight naturally increase with age?
Yes, gradual weight gain is common with age due to slowing metabolism and declining muscle mass. However, gaining 0.5–1 kg per year is typical, not inevitable. Staying active and maintaining healthy eating habits can minimise unwanted weight gain across life stages.
What is a healthy weight for my age in the UK?
Healthy weight in the UK is determined by BMI (18.5–24.9), not by age. Use our free weight converter and BMI calculator to find your healthy weight range for your height. Your GP can also advise on what's healthy for you personally.
Why does metabolism slow with age?
Metabolism slows because muscle mass declines naturally after age 30 (sarcopenia), reducing how many calories your body burns at rest. Hormonal changes, especially in women during menopause, also contribute. Regular strength training helps slow this decline.
Is it harder to lose weight as you get older?
Weight loss becomes slightly slower with age due to lower metabolism, but it's absolutely achievable at any age. A calorie deficit of 500 kcal daily still typically results in 0.5 kg weekly loss. Your GP can advise on safe weight loss strategies suited to your age and health.
Should older adults try to reach a lower BMI?
Healthy BMI (18.5–24.9) remains the target at any age according to NHS guidance. However, your GP may consider individual factors like muscle mass and health conditions. Very low weight in older age can increase frailty risk, so speak to your GP about what's right for you.
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.