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 Do You Find Out Your BMI?
Finding out your BMI is straightforward — you need 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 standard health screening tool to help you understand whether your weight falls within a healthy range for your height. This guide explains how to calculate your BMI, what the NHS BMI categories mean, and when you might want to discuss your results with your GP. You can also use our free BMI calculator above to find your BMI instantly.
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.
Understanding the BMI Formula and NHS Categories
The BMI formula is: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73)² = 23.4, which falls in the healthy weight range. The NHS uses four main BMI categories:
- Under 18.5: Underweight
- 18.5–24.9: Healthy weight
- 25.0–29.9: Overweight
- 30.0 and above: Obese
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these groups face higher health risks at lower BMI levels. A healthy BMI range for these populations is 18.5–22.9 instead of 18.5–24.9. NICE guidance emphasises that BMI is a useful screening tool, but it has limitations — it does not distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. Your GP can provide personalised context about what your BMI means for your individual health.
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 falls outside the healthy range, the NHS offers support through its weight management pathway. Your GP can discuss your weight in a non-judgmental way and signpost you to appropriate resources. The NHS operates a four-tier weight management system: Tier 1 includes self-help digital tools and community programmes; Tier 2 offers primary care-based behaviour change support; Tier 3 provides specialist multidisciplinary weight management services where prescription medications may be considered; and Tier 4 covers bariatric surgery for severe obesity with significant health complications. You can use our free BMI calculator above to check your status, and if you're concerned about your weight, arrange a consultation with your GP to discuss your personal health context and available NHS support options.
- 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 in simple terms?
BMI = weight in kilograms ÷ (height in metres × height in metres). For example, if you weigh 80kg and are 1.75m tall, your BMI is 80 ÷ (1.75 × 1.75) = 26.1. Use our free BMI calculator above to work this out instantly without a UK pharmacy calculation.
What is a healthy BMI according to the NHS?
The NHS defines a healthy BMI as 18.5–24.9 for most UK adults. For South Asian, Chinese, Black African, or Black Caribbean adults, the healthy range is 18.5–22.9 due to higher health risks at lower BMI levels. Your GP can advise on what's healthy for you personally.
Does BMI account for muscle mass?
No — BMI does not distinguish between muscle and fat. Athletes or very muscular individuals may have a high BMI but low body fat. This is why the NHS recommends discussing your BMI with your GP rather than relying on it alone. Waist circumference is also important for assessing health risk.
When should I contact my GP about my BMI?
If your BMI is above 25 (or above 23 for South Asian backgrounds), or if you have concerns about your weight and health, it's worth discussing with your GP. They can provide personalised guidance, check for weight-related health conditions, and signpost you to NHS weight management support if appropriate.
What is the NHS weight management pathway?
The NHS offers four tiers of support: Tier 1 includes self-help tools and community programmes; Tier 2 offers GP-based behaviour change support; Tier 3 provides specialist weight management services and prescription medications; Tier 4 covers bariatric surgery. Your GP can discuss which tier is appropriate for your situation.
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.