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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Weight Formula — Calculate Your Healthy Weight Range
A weight formula is a mathematical calculation used to assess whether your weight falls within a healthy range for your height and age. In the UK, the most common formula is BMI (Body Mass Index), which divides your weight in kilograms by your height in metres squared. Understanding weight formulas helps you track your health and identify whether weight management might be beneficial. Use our free BMI calculator above to work out your personal score instantly, and explore evidence-based weight management strategies aligned with NHS guidance.
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.
Common Weight Formulas Used in UK Health Guidance
BMI (Body Mass Index) is the primary weight formula recommended by the NHS. The formula is: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your BMI = 70 ÷ (1.75)² = 22.9, which falls in the healthy weight range (18.5–24.9). The NHS categorises BMI as: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), obese (30.0–34.9), and severely obese (40.0+).
Ethnicity matters: For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — healthy weight begins at 18.5 and ends at 22.9, because these groups face higher health risks at the same BMI levels.
- BMI is a screening tool, not a diagnosis
- BMI does not account for muscle mass or fat distribution
- Waist circumference is also important — men over 94cm and women over 80cm have increased health risk
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.
Ideal Weight and Weight Management Formulas
Several formulas estimate ideal body weight, though there is no single "correct" weight for everyone. The Devine Formula is widely used: Men = 50kg + 2.3kg per inch over 5ft; Women = 45.5kg + 2.3kg per inch over 5ft. However, ideal weight varies by frame size, muscle mass, and individual health factors. The NHS recommends using your BMI range as your primary guide — not a fixed number. For sustainable weight loss, NHS health guidance emphasises a calorie deficit of around 500 kcal per day, resulting in approximately 0.5–1kg loss per week. Use our free weight converter to switch between kg, stone, and pounds, and track progress with our progress tracker tool.
- 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 the most accurate weight formula for UK health assessment?
BMI (Body Mass Index) is the standard weight formula recommended by the NHS and used across UK healthcare. It divides weight in kilograms by height in metres squared. However, BMI has limitations — it doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. Your GP can assess whether your weight is healthy for you individually.
How do I calculate my healthy weight range using a formula?
For a healthy BMI range (18.5–24.9), multiply your height in metres squared by both 18.5 and 24.9. For example, at 1.75m tall: lower bound = 18.5 × (1.75)² = 56.6kg; upper bound = 24.9 × (1.75)² = 76.1kg. Use our free BMI calculator on this page for an instant calculation specific to your measurements.
What's the difference between ideal weight and healthy weight range?
Healthy weight range is based on BMI (18.5–24.9) and applies to most adults. Ideal weight formulas like Devine's estimate a specific target, but vary by muscle mass and frame size. The NHS recommends using your BMI range as your primary guide, as it's more evidence-based and flexible than a single target weight.
Does the weight formula change for different ages or ethnicities?
BMI formula is the same for all adults, but interpretation differs by ethnicity. South Asian, Chinese, Black African, and Black Caribbean adults have lower healthy BMI thresholds (18.5–22.9 instead of 18.5–24.9) because they face higher health risks at the same BMI. Always discuss your personal health context with your GP.
What weight loss formula does the NHS recommend?
The NHS recommends a calorie deficit of approximately 500 kcal per day, which typically results in losing 0.5–1kg per week. This is considered a safe, sustainable rate. For faster or medically supervised weight loss, your GP can refer you to a tier 3 specialist weight management service, where prescription weight management options may be discussed.
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.