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 Test Your BMI — The NHS Way
Testing your BMI is straightforward and takes just two measurements: your weight and height. The BMI formula divides your weight in kilograms by your height in metres squared. The NHS uses BMI as a screening tool to assess whether your weight falls within a healthy range for your height. This guide explains how to calculate your BMI accurately, what the NHS BMI categories mean, and when you should speak to your GP about your results. You can test your BMI manually or use our free BMI calculator above for gradual improvement.
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 Formula and Categories
The BMI formula is: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your BMI would be 70 ÷ (1.75)² = 22.9. According to NHS BMI categories UK, this falls in the healthy weight range.
The NHS BMI range divides adults into these categories:
- Underweight: Below 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25.0 to 29.9
- Obese (Class I): 30.0 to 34.9
- Obese (Class II): 35.0 to 39.9
- Severely obese (Class III): 40.0 and above
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — a healthy BMI starts at 18.5 and overweight begins at 23.0. These lower thresholds reflect higher health risks at standard BMI levels for these groups.
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 and When To Seek Help
The NHS provides a structured weight management pathway depending on your BMI and health. If your BMI is above 25, your GP may discuss your weight and lifestyle. For a BMI of 30 or above (or 27+ with weight-related conditions), you may be referred to specialist weight management services. The NHS also notes that BMI has limitations — it doesn't distinguish muscle from fat or account for where fat is stored. Waist measurement and overall fitness matter too. Use our free BMI calculator alongside the weight converter on this page to understand your full health context, then discuss results with your GP for personalised guidance.
- 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's the easiest way to test my BMI?
Use our free BMI calculator above — it calculates instantly. Or measure your weight in kilograms and height in metres, then divide weight by height squared. For example, 70kg ÷ (1.75m)² = BMI of 22.9. The calculator removes the maths.
What BMI range does the NHS consider healthy?
The NHS considers 18.5 to 24.9 as a healthy BMI for most UK adults. For South Asian, Chinese, Black African, and Black Caribbean adults, the healthy range is 18.5 to 22.9. Your GP can explain what your personal BMI means for your health.
Should I worry if my BMI is in the overweight category?
Not necessarily — BMI is a screening tool, not a diagnosis. It doesn't account for muscle mass, fitness level, or where fat is stored. A high BMI may indicate health risks, but your GP will consider your full health picture, including blood pressure, blood sugar, and lifestyle.
When should I see my GP about my BMI?
Speak to your GP if your BMI is consistently above 25, if you've noticed weight gain, or if you have weight-related health concerns like breathlessness or joint pain. Your GP can assess your individual risk and discuss next steps, including referral to weight management services if appropriate.
What are the limitations of BMI testing?
BMI doesn't distinguish between muscle and fat — athletes may have a high BMI but be very fit. It also ignores where fat is stored (waist fat is riskier) and doesn't account for age, bone density, or ethnicity-specific health thresholds. Use BMI alongside waist measurement and discuss results with your GP for context.
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.