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
What Is the Ideal Body Weight Equation?
There is no single "ideal" body weight for everyone — it depends on your height, age, muscle mass, and individual health factors. However, health professionals use standardised equations to estimate a healthy weight range. The most common UK and international formulas are the Devine equation, Robinson equation, and Miller equation. These provide a starting point, but NHS guidance emphasises that a healthy BMI between 18.5 and 24.9 is more useful for assessing whether your weight supports good health. Individual results and body composition vary significantly, so these equations are best used alongside a BMI calculator and personalised GP advice.
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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.
Common Ideal Body Weight Formulas
Devine Formula (most widely used):
- Men: 50 kg + 2.3 kg per inch over 5 feet
- Women: 45.5 kg + 2.3 kg per inch over 5 feet
Robinson Formula:
- Men: 52 kg + 1.9 kg per inch over 5 feet
- Women: 49 kg + 1.7 kg per inch over 5 feet
Miller Formula:
- Men: 56.2 kg + 1.41 kg per inch over 5 feet
- Women: 53.1 kg + 1.36 kg per inch over 5 feet
These formulas were developed from population averages and do not account for muscle mass, bone density, or individual variation. For example, an athlete with significant muscle may fall outside the "ideal" range but still be healthy. Use our free BMI calculator above to check where your current weight falls within NHS healthy weight guidance, which is often more practical than theoretical ideal weight equations.
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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.
Why These Equations Have Limitations
Ideal body weight equations provide a reference point, but they cannot replace individualised health assessment. They do not distinguish between muscle and fat — someone who weight trains may weigh more than the equation suggests but have excellent body composition. They also ignore ethnicity, age, and medical history. The NHS prefers to use BMI and waist circumference as practical screening tools. For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds apply because these groups face higher health risks at the same weight. Rather than chasing a specific number from an equation, focus on achieving a healthy BMI range (18.5–24.9 for most adults) and maintaining good fitness and nutrition. Your GP can give personalised UK health advice tailored to your circumstances.
- 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 height is the Devine formula based on?
The Devine formula uses 5 feet (60 inches) as the baseline and adds weight based on each additional inch of height. It was developed from population data and remains widely used by health professionals, though it is one of several approaches.
Is ideal body weight the same as healthy weight?
Not exactly. Ideal body weight is a calculated reference point, while healthy weight is determined by your individual BMI, fitness, and health status. NHS guidance focuses on BMI ranges (18.5–24.9) rather than a single "ideal" number, as muscle mass and distribution matter significantly.
How does ideal body weight compare to my BMI?
BMI may be more practical than ideal body weight equations. Calculate your BMI using the free BMI calculator on this page — if it falls between 18.5 and 24.9, you are within NHS healthy weight guidance, regardless of what an ideal weight equation suggests.
Can I use ideal body weight for weight loss planning?
You can use it as a rough guide, but weight loss is better planned using calorie deficit and sustainable lifestyle changes. The NHS recommends losing 0.5–1 kg per week. Our free weight converter and BMI calculator help you set realistic goals based on your current height and weight.
Do ideal body weight equations apply to children and teenagers?
No. Children use age and sex-specific growth centile charts, not adult formulas. Always consult your GP or use the NHS Healthy Weight Calculator for children — adult equations do not apply.
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.