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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Understanding Your Body Weight in the UK
Your body weight is one of the most basic health measurements, but understanding what constitutes a healthy weight for you personally requires more than just a number on the scales. In the UK, the NHS uses Body Mass Index (BMI) as the primary screening tool to assess whether your weight falls within a healthy range for your height. However, body weight is influenced by many factors including age, muscle mass, genetics, and underlying health conditions. This guide explains how the NHS assesses healthy body weight, how to measure yours accurately, and what resources are available to help you understand your personal weight management needs.
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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 the NHS Assesses Healthy Body Weight
The NHS uses Body Mass Index (BMI) as the main tool to assess whether body weight is in a healthy range. BMI is calculated by dividing your weight in kilograms by your height in metres squared. According to NHS guidance, a healthy BMI for most adults is between 18.5 and 24.9.
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight
- 25.0–29.9: Overweight
- 30.0 and above: Obese
However, BMI has important limitations. It does not distinguish between muscle and fat — athletes may have a high BMI despite low body fat. For adults of South Asian, Chinese, Black African, and Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher health risks at the same BMI levels. Your GP can assess your personal body weight in the context of your overall health, family history, and any existing health conditions. Use our free BMI calculator above to check where your current body weight sits, and discuss any concerns with your healthcare provider.
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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.
Measuring and Tracking Your Body Weight
Accurate body weight measurement requires consistent conditions — weigh yourself at the same time each day, ideally in the morning before eating, on the same scales. Weight naturally fluctuates by 1–2 kg day-to-day due to hydration, food intake, and hormonal changes, so focus on trends over weeks rather than daily variations. The NHS recommends weighing yourself weekly for weight management purposes. Our free progress tracker allows you to log your weight over time and visualise patterns, helping you understand whether your weight management approach is working. For healthy weight management in the UK, NHS guidance emphasises sustainable approaches combining modest dietary changes with increased physical activity. If you need support with weight management, your GP can refer you to tier 2 or tier 3 NHS weight management services, or discuss whether prescription weight loss support might be appropriate for you.
- 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.
What is considered a healthy body weight in the UK?
The NHS defines healthy body weight as a BMI between 18.5 and 24.9 for most adults. However, what constitutes a healthy weight for you personally depends on your height, age, muscle mass, and overall health. For specific guidance on your own healthy weight range, use our free BMI calculator or speak with your GP.
Why does body weight fluctuate day-to-day?
Daily weight fluctuations of 1–2 kg are normal and caused by variations in hydration, food intake, hormones, and digestive contents. This is why the NHS recommends weighing yourself weekly and tracking trends over time rather than focusing on daily changes.
How often should I weigh myself for health monitoring?
The NHS recommends weighing yourself once a week at the same time of day for consistent monitoring. Try our free progress tracker to log weekly measurements and see your long-term trends, which is more meaningful than daily fluctuations.
Does a high BMI always mean excess body fat?
No. BMI does not distinguish between muscle and fat, so very muscular individuals or athletes may have a high BMI despite low body fat. Your GP can assess your body weight in context of your overall health, waist circumference, and fitness level.
What should I do if I'm concerned about my body weight?
Start by speaking with your GP, who can assess your personal situation and refer you to appropriate support. The NHS offers free weight management resources, tier 2–3 services, and in some cases prescription weight loss support depending on your BMI and health conditions.
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.