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
How to Calculate BMI from kg — NHS Guidance
Calculating your BMI from kilograms is straightforward using the standard formula: weight (kg) divided by height in metres squared. The NHS uses this simple calculation to assess whether your weight falls into a healthy range. Understanding your BMI is the first step towards managing your health, though it's important to recognise that BMI has limitations and doesn't account for muscle mass or where fat is stored on your body. Use our free BMI calculator above to find your BMI instantly, or follow the NHS formula yourself.
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.
NHS BMI Categories and Healthy Weight Ranges
The NHS categorises BMI into clear ranges to help you understand your weight status. A healthy BMI is between 18.5 and 24.9 kg/m². If your BMI falls between 25.0 and 29.9, you're classified as overweight. A BMI of 30.0 or above indicates obesity, divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+).
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds due to increased health risks at the same BMI level. These groups should aim for a healthy BMI between 18.5 and 22.9.
- Healthy weight (BMI 18.5–24.9): Lower risk of weight-related health conditions
- Overweight (BMI 25–29.9): Increased risk of type 2 diabetes and heart disease
- Obese (BMI 30+): Significantly elevated health risks
Calculate your personal BMI using the calculator on this page to see which category you fall into.
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.
NHS Weight Management Pathway and When to Seek Help
The NHS offers a structured weight management pathway with support at different levels. Your GP is your starting point—they can assess your health, discuss lifestyle changes, and refer you to appropriate services if needed. If your BMI exceeds 30, or you're overweight with weight-related health conditions like type 2 diabetes or high blood pressure, your GP may recommend a specialist tier 3 weight management service.
Weight management isn't just about numbers—the NHS focuses on sustainable changes including balanced eating, increased physical activity, and behaviour support. Even a 5–10% reduction in body weight can significantly improve your health markers. Don't delay talking to your GP if you're concerned about your weight or health.
- 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 BMI formula and how do I calculate it from kg?
The BMI formula is weight (kg) divided by height (metres) squared. For example, if you weigh 75 kg and are 1.75 metres tall, your BMI = 75 ÷ (1.75 × 1.75) = 24.5. The free BMI calculator on this page does this instantly for you without a UK pharmacy calculation.
Is a BMI between 18.5 and 24.9 considered healthy by the NHS?
Yes, the NHS defines 18.5 to 24.9 as a healthy BMI range for most UK adults. However, people of South Asian, Chinese, Black African, or Black Caribbean heritage should aim for 18.5 to 22.9 due to higher health risks at the same BMI level.
What does the NHS recommend if my BMI is over 30?
If your BMI is 30 or above, the NHS recommends speaking to your GP. You may be eligible for support from weight management services, including lifestyle advice, behaviour change programmes, and in some cases, prescription medication alongside diet and exercise changes.
Does BMI account for muscle mass and fitness?
No, BMI does not distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite low body fat. The NHS recognises this limitation and recommends considering waist circumference and overall health alongside BMI for a complete picture.
Can I use the same BMI categories if I'm pregnant or very elderly?
BMI is less accurate during pregnancy and in elderly adults due to changes in body composition. Speak to your GP or midwife for personalised guidance during pregnancy, or discuss age-appropriate health assessments with your doctor if you're elderly.
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.