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, Weight and Height — UK Health Context
Your age, weight, and height all interact to determine your health risk. In the UK, weight management isn't just about the number on the scale — it's about understanding what a healthy weight means at different life stages. The NHS provides guidance on healthy weight ranges across all ages, and tools like our free BMI calculator can help you assess where you fall. This guide explains how these three factors work together and what NHS guidance recommends.
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.
How Age Affects Weight and Health in the UK
Age significantly influences how your body manages weight and metabolic health. In childhood and adolescence, growth and development are primary focuses — the NHS uses age and sex-specific growth charts rather than standard BMI categories for children under 18. In adulthood (18–65), standard NHS BMI categories apply: healthy weight is between 18.5 and 24.9, with higher risks at BMI 25 and above. After age 65, some studies suggest slightly higher BMI may be protective, though maintaining activity and good nutrition remains crucial. Your GP can provide personalised guidance based on your age and individual health profile. Additionally, age affects metabolism, muscle mass, and risk of weight-related conditions like type 2 diabetes and heart disease — all factors your healthcare provider considers when discussing weight management.
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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.
Height, Weight and Your Healthy Weight Range
Height is the foundation for calculating healthy weight using BMI and weight management guidance. The NHS healthy weight calculator uses both your height and weight to determine your BMI category. For example, a healthy weight range for an adult of 5ft 8in (173cm) is approximately 55–74kg (8st 10lbs to 11st 10lbs). Use our free weight converter to switch between kg, stone, and pounds easily. For South Asian, Chinese, Black African, or Black Caribbean adults, the NHS recommends lower thresholds due to higher cardiovascular risk at standard BMI levels — your GP can advise whether adjusted targets apply to you. Remember that healthy weight varies by frame size, muscle mass, and individual health conditions.
- 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?
Yes. Children use growth charts; adults use BMI categories. After age 65, some research suggests slightly different risk thresholds, but maintaining a healthy weight remains important at all ages. Your GP can advise what's healthy for your specific age and health profile.
How do I calculate my healthy weight range using my height?
Use the formula: healthy BMI is 18.5–24.9. Multiply your height in metres squared by 18.5 (lower range) and 24.9 (upper range) to get your weight range in kg. Our free BMI calculator above does this instantly — just enter your height and weight.
What's the difference between height and weight in BMI?
Height and weight work together in BMI. BMI = weight (kg) ÷ height (metres)². Height is squared, so small height changes significantly affect your healthy weight range. Two people of different heights can have very different healthy weight ranges.
Can I use an online weight converter to check my UK healthy weight?
Yes. Our free weight converter above converts between kg, stone, and pounds. Once you know your weight in your preferred unit, use our BMI calculator to see if you're in the healthy range for your height according to NHS guidelines.
Should I discuss weight with my GP?
Yes, especially if you're concerned about changes with age. Your GP can assess whether your weight is healthy for your age, height, and individual health conditions — and can discuss weight management support if needed, including NHS weight management services or prescription options where appropriate.
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.