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
What Does "BMI Checked" Mean?
When your BMI is checked, you're measuring how your weight relates to your height — a screening tool used by the NHS to assess whether you're in a healthy weight range. Your result falls into a specific category: underweight, healthy weight, overweight, obese, or severely obese. Understanding your BMI and what it means for your health is an important first step in managing your wellbeing. Use our free BMI calculator above to check your personal BMI instantly, and this guide will help you interpret your result.
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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.
Understanding Your BMI Result and NHS Categories
Once your BMI has been checked, it's classified into one of five NHS BMI categories. A healthy BMI ranges from 18.5 to 24.9 — this is where the health risks associated with excess weight are lowest. If your BMI formula result falls between 25.0 and 29.9, you're classified as overweight; 30.0 to 34.9 is obese Class I; 35.0 to 39.9 is obese Class II; and 40.0 or above is severely obese.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI thresholds are lower due to higher health risks at similar weights. For these groups, a healthy BMI is 18.5 to 22.9, and overweight begins at 23.0. Your GP can explain which category applies to you and what it means for your individual health.
- 18.5–24.9: Healthy weight
- 25.0–29.9: Overweight
- 30.0–34.9: Obese Class I
- 35.0–39.9: Obese Class II
- 40.0+: Severely obese
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.
BMI Limitations and What Else Matters
While checking your BMI is useful, it's important to understand that BMI limitations exist. BMI doesn't distinguish between muscle and fat — an athlete with high muscle mass might have a high BMI but low body fat. It also doesn't account for where fat is stored; waist measurement is equally important for assessing health risk. For older adults, BMI may be less accurate due to age-related muscle loss. Use our weight converter to track changes in your weight across different units, and discuss your individual health picture with your GP rather than relying on BMI alone.
- 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 is it calculated?
BMI is calculated by dividing your weight in kilograms by your height in metres squared (kg ÷ m²). For example, someone weighing 70kg and 1.75m tall would have a BMI of 22.9. Our BMI calculator above does this instantly for you in UK measurements.
Is a healthy BMI the same for everyone in the UK?
Not quite. The standard NHS healthy BMI range is 18.5–24.9 for most adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is lower (18.5–22.9) because these groups face higher cardiovascular and diabetes risk at similar BMI levels.
What does it mean if my BMI has been checked and I'm overweight?
An overweight BMI (25.0–29.9) suggests your health could benefit from modest lifestyle changes. This doesn't mean you're unhealthy, but reducing weight by even 5–10% can improve blood pressure, blood sugar, and joint health. Speak to your GP about realistic goals.
Can BMI be inaccurate?
Yes. BMI doesn't account for muscle mass, bone density, or where fat is stored. Athletes often have high BMI but low body fat. Waist circumference (over 94cm for men, 80cm for women indicates increased risk) is a helpful additional measure alongside BMI.
Why are BMI categories different for South Asian adults?
Research shows South Asian, Chinese, Black African, and Black Caribbean populations have higher risk of type 2 diabetes and heart disease at lower BMI levels. The NHS recommends lower thresholds (healthy: 18.5–22.9) for these groups to identify risk earlier.
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.