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
Calculate How Much Weight Loss You Need
Working out how much weight loss you need starts with understanding your ideal weight for your height. The NHS provides clear healthy weight ranges based on BMI (Body Mass Index), and our free BMI calculator makes it easy to find where you stand and what your target should be. Whether you want to know your healthy weight for your height or how much weight loss would benefit your health, this guide explains exactly how to calculate it using UK health standards.
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 to Use the BMI Calculator to Find Your Ideal Weight
Our free BMI calculator above instantly shows you your current BMI and compares it to the NHS healthy weight range for your height. Enter your weight (in stone, pounds, or kilograms) and height, and the calculator displays:
- Your current BMI number
- Which NHS category you fall into (underweight, healthy, overweight, or obese)
- The healthy weight range for your height — showing the minimum and maximum weight for a healthy BMI
- How much weight loss (if any) would move you into the healthy range
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends slightly lower thresholds for optimal health. The calculator uses the standard adult BMI categories: 18.5–24.9 is healthy, 25–29.9 is overweight, and 30+ is obese. Remember that BMI is a screening tool — it doesn't account for muscle mass or where fat is stored, so your GP can provide personalised guidance alongside your results.
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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.
What to Do If You're Above a Healthy Weight
If the BMI calculator shows you're above the healthy weight range, the next step is practical planning. The NHS recommends losing weight at a steady rate of 0.5 to 1 kg per week — this typically requires a calorie deficit of around 500 kcal daily and is more sustainable than rapid loss. Even losing just 5–10% of your current body weight can bring meaningful health benefits, including improved blood pressure, better blood sugar control, and reduced joint strain. Our free progress tracker helps you log weight changes over time. For support, ask your GP about NHS weight management programmes in your area, or consider speaking with a registered dietitian. If you have multiple weight-related health conditions, your GP may discuss other options available to 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 does the BMI calculator tell me?
The BMI calculator shows your Body Mass Index number and which NHS weight category you fall into. It also displays the healthy weight range for your exact height, so you can see exactly how much weight loss (if any) would move you into that range. It's a screening tool only — always discuss results with your GP for personalised advice.
What is the healthy weight range for my height?
Your healthy weight range depends on your height and is based on a BMI of 18.5–24.9 according to NHS guidelines. For example, at 5ft 8in (173cm), a healthy weight is roughly 55–74kg (8st 10lbs–11st 10lbs). Use the BMI calculator on this page to find your exact healthy range instantly — it's unique to your height.
How much weight should I aim to lose per week?
The NHS recommends losing 0.5–1 kg (1–2 lbs) per week for sustainable, healthy weight loss. This typically requires a calorie deficit of around 500 kcal daily through diet and activity changes. Faster weight loss is possible but increases muscle loss risk and is not recommended without medical supervision.
Does BMI apply to me if I'm very muscular or elderly?
BMI has limitations. It doesn't distinguish between muscle and fat, so very muscular individuals may have a high BMI but low body fat. For elderly people, muscle naturally decreases with age and BMI may not be accurate. Your GP can assess your personal health and advise whether BMI is the right measure for you.
What should I do if my BMI shows I need to lose weight?
Start with small, sustainable changes: reduce portion sizes, increase physical activity, and stay hydrated. Ask your GP about NHS weight management services in your area — many areas offer free, evidence-based support. Use our progress tracker to log your journey. If you have health conditions, discuss any major dietary changes with your GP first.
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.