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 BMI in Kilos — NHS Health Guidance
BMI (body mass index) is a screening tool that uses your weight in kilos and height to assess whether you're in a healthy weight range. The NHS uses the BMI formula to help identify health risks linked to excess weight. Understanding your BMI in kilos is straightforward — and knowing where you sit on the NHS BMI scale can help you decide if lifestyle changes or a chat with your GP might be helpful. This guide explains the NHS BMI categories, what the numbers mean, and what happens next if you're concerned about your weight.
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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.
NHS BMI Categories and What They Mean
The NHS BMI formula divides your weight in kilos by your height in metres squared. Using this calculation, the NHS has established five official BMI categories that help identify health risk:
- Underweight: BMI below 18.5 — may indicate nutritional concerns
- Healthy weight: BMI 18.5 to 24.9 — lower health risk from weight-related conditions
- Overweight: BMI 25.0 to 29.9 — increased risk of type 2 diabetes and heart disease
- Obese (Class I): BMI 30.0 to 34.9 — significant health risks
- Obese (Class II): BMI 35.0 to 39.9 — higher health risks
- Severely obese (Class III): BMI 40.0+ — substantial health risks requiring medical support
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these populations face higher diabetes and cardiovascular risk at the same BMI levels. For these groups, a healthy weight sits between 18.5 and 22.9, and the overweight threshold begins at 23.0.
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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.
NHS Weight Management Support — What's Available
If your BMI falls outside the healthy range, the NHS offers structured support through its weight management pathway. Your GP can refer you to tier 3 specialist weight management services where you'll receive tailored advice on diet, physical activity, and behaviour change. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results. Some patients qualify for prescription weight loss medication through NHS specialist services, though availability varies by region. Start by speaking to your GP about your weight health — they can assess your individual situation, discuss any weight-related health conditions, and signpost you to appropriate support.
- 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.
How do I calculate my BMI in kilos?
Use the BMI formula: weight in kilos divided by height in metres squared. For example, if you weigh 70kg and are 1.75m tall, your BMI is 70 ÷ (1.75 × 1.75) = 22.9 (healthy weight range). Use our free BMI calculator above to find your exact BMI instantly — just enter your weight in kilos and height.
What's considered a healthy BMI in kilos?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower healthy range of 18.5 to 22.9 because these groups have higher health risks at higher BMI levels.
Why does the NHS use BMI if it has limitations?
BMI is a quick, practical screening tool that helps identify health risk at population level. However, BMI has real limitations — it doesn't distinguish muscle from fat, doesn't account for where fat is stored, and may be less accurate for elderly adults or athletes. Your GP considers BMI alongside other factors like waist circumference and health history.
Should I worry if my BMI is in the overweight category?
An overweight BMI (25.0 to 29.9) suggests increased risk of conditions like type 2 diabetes and heart disease, but it doesn't mean you will definitely develop these. Your GP can assess your individual risk based on your health history, blood pressure, cholesterol, and other factors. Even a 5–10% reduction in weight can improve health outcomes.
How do I get NHS support if my BMI is above the healthy range?
Book an appointment with your GP to discuss your weight and health. Your GP can assess whether you need support and refer you to NHS weight management services (tier 3), where you'll receive structured advice on diet, activity, and behaviour change. Some patients qualify for prescription weight loss medication through these specialist services.
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.