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
BMI Test Online — NHS Health Guidance
A BMI test online is a quick way to check whether your weight falls within a healthy range according to NHS guidelines. BMI (Body Mass Index) is calculated using your height and weight, and the NHS uses it as a screening tool to assess health risk. While BMI has limitations — it doesn't distinguish between muscle and fat, for example — it remains the standard measurement used by UK healthcare services. Understanding your BMI range and what the NHS recommends can help you make informed decisions about your health. Use our free BMI calculator above to find your personal BMI instantly, and explore what it means for you.
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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.
NHS BMI Categories and What They Mean
The NHS BMI formula is weight (kg) divided by height (m) squared. According to NHS guidance, BMI ranges are divided into clear categories that help identify health risks:
- Underweight: BMI below 18.5 — may indicate nutritional concerns
- Healthy weight: BMI 18.5 to 24.9 — associated with lowest health risks
- Overweight: BMI 25.0 to 29.9 — increased health risks begin to emerge
- 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 and above — substantial health risks
Importantly, the NHS recognises that adults of South Asian, Chinese, Black African, and Black Caribbean backgrounds face higher health risks at lower BMI thresholds. For these groups, the healthy BMI range starts at 18.5 but extends only to 22.9, and overweight BMI begins at 23.0.
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 offers a structured weight management pathway with support at every level. If your healthy BMI threshold indicates you may benefit from support, your GP can refer you to NHS services. NICE guidance recommends that adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions, should be offered behaviour change support. For some patients, prescription weight loss treatment may be appropriate — this is typically offered through specialist tier 3 weight management services. The NHS also emphasises that even a 5–10% reduction in body weight can significantly improve health outcomes, including blood pressure, blood sugar control, and cardiovascular risk. Your GP is the best starting point for personalised advice.
- 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 used by the NHS?
The NHS BMI formula is weight (kg) divided by height (m) squared. For example, a person weighing 70kg who is 1.75m tall would have a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy weight range. Use our free BMI calculator to work this out instantly without a UK pharmacy calculation.
Why does the NHS use different BMI thresholds for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean descent have higher risks of type 2 diabetes and heart disease at lower BMI levels. The NHS therefore recommends lower BMI thresholds for these groups — healthy weight extends to BMI 22.9 rather than 24.9 — to identify risk earlier and offer support sooner.
What are BMI limitations and why does the NHS acknowledge them?
BMI doesn't distinguish between muscle and fat, so athletes may have high BMI but low body fat. It also doesn't account for fat distribution — where you carry weight matters for health. The NHS recognises these limitations and recommends combining BMI assessment with waist measurement and overall health context when making health decisions.
When should I contact my GP about my BMI?
If your BMI falls outside the healthy range (18.5–24.9 for most adults, or 18.5–22.9 for South Asian and other specified groups), or if you have concerns about your weight and health, speak to your GP. They can assess your individual situation, discuss health risks, and refer you to NHS weight management services if appropriate.
Does the NHS offer free weight loss support?
Yes. The NHS offers a structured weight management pathway including self-help resources, GP-based behaviour change support, and specialist services. Access varies by region and ICB. Your GP can refer you to services in your area. For some patients, prescription weight loss treatment may be available through specialist NHS weight management services, though waiting times vary significantly.
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.