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 Your BMI — NHS Guidance
BMI (Body Mass Index) is a simple measurement that helps assess whether your weight falls into a healthy range for your height. The NHS uses BMI calculations as a screening tool to identify whether adults may be at risk from weight-related health conditions. Calculating your own BMI takes just seconds using your weight in kilograms and height in metres — and understanding your BMI range is an important first step in managing your health. Use our free BMI calculator above to find your personal BMI instantly, alongside guidance on what it means for you.
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 recognises four main BMI categories for adults, based on extensive clinical research:
- Healthy weight: BMI 18.5 to 24.9 — the target range where weight-related health risks are lowest
- 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 present
- Obese (Class II and III): BMI 35.0 and above — very high risk of serious weight-related conditions
To calculate your healthy BMI range for your height, the NHS formula divides your weight in kilograms by your height in metres, squared. For example, at 5ft 8in (1.73m), a healthy BMI falls between 55kg and 75kg. However, BMI has important limitations — it does not distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. The NHS recommends also measuring waist circumference alongside BMI for a fuller picture of 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.
NHS Weight Management Support and When to Seek Help
If your BMI calculation shows you are overweight or obese, the NHS offers a four-tier weight management pathway. Tier 1 includes self-help tools and community programmes — MyWeightCheck's free BMI calculator and weight converter support this self-assessment stage. Tier 2 offers GP-led behaviour change support, including the NHS Weight Loss Plan. Tier 3 provides specialist multidisciplinary weight management services where prescription medications may be considered. Most adults can start with lifestyle changes: the NHS recommends losing weight at a safe rate of 0.5 to 1kg per week. Contact your GP if you have a BMI above 30, or if you have a BMI of 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea — your GP can assess your individual situation and discuss the right support for 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.
How do I calculate my BMI accurately?
Use the formula: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4. Our free BMI calculator above does this instantly — just enter your weight and height.
What is a healthy BMI according to the NHS?
The NHS defines a healthy BMI as 18.5 to 24.9 for most adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, a healthy BMI starts at 18.5 and ends at 22.9, because these groups face higher health risks at higher BMI levels.
Does a high BMI always mean I'm unhealthy?
BMI is a useful screening tool but has limitations. It cannot distinguish between muscle and fat — athletes may have a high BMI but be very fit. BMI also does not account for where fat is stored. The NHS recommends measuring waist circumference alongside BMI, and consulting your GP for personalised health advice.
When should I contact my GP about my BMI?
Contact your GP if your BMI is 30 or above, or if it is 27–29.9 and you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess whether you would benefit from weight management support.
Can BMI calculations be different for children?
Yes — BMI for children is calculated the same way but interpreted differently. Children's BMI uses age and sex-specific growth charts (UK90 reference), not adult categories. Always consult your GP or use the NHS Healthy Weight Calculator for children instead.
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.