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 Calculate BMI Formula
BMI (Body Mass Index) is calculated using a straightforward formula: divide your weight in kilograms by your height in metres squared. This gives you a single number that healthcare professionals use to screen for weight categories. The NHS uses BMI as a key health indicator, though it's important to understand both how to calculate it and what its limitations are. Use our free BMI calculator above to find your gradual improvement, or follow the a UK pharmacy calculation steps below.
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.
The BMI Formula and How to Calculate It
The BMI formula in metric (SI) units is: BMI = weight (kg) ÷ height (m)²
To calculate manually: measure your weight in kilograms and your height in metres. Convert centimetres to metres by dividing by 100 (for example, 170 cm = 1.70 m). Square your height (multiply it by itself), then divide your weight by this squared value.
Example: A person weighing 70 kg and 1.75 m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI
The NHS BMI range categories for UK adults are: Underweight (below 18.5), Healthy weight (18.5–24.9), Overweight (25.0–29.9), Obese Class I (30.0–34.9), Obese Class II (35.0–39.9), and Severely obese (40.0+). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy BMI threshold starts at 18.5 but the overweight threshold begins at 23.0 instead of 25.0.
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.
BMI Limitations and What Else Matters
BMI is a useful screening tool but has significant BMI limitations—it doesn't distinguish between muscle and fat, so very athletic individuals may have a high BMI despite low body fat. It also ignores where fat is stored; waist circumference is equally important for health risk. BMI is less accurate for older adults (who lose muscle naturally), pregnant women, and children (who require age-specific growth charts).
The NHS recommends combining BMI assessment with other health measures: waist circumference (healthy limit under 94 cm for men, 80 cm for women), blood pressure, cholesterol, and blood sugar levels. Your GP can provide personalised interpretation of your BMI in the context of your individual health. Convert your weight between kg, stone, and pounds using our free weight converter to check your measurements in your preferred units.
- 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 a healthy BMI according to the NHS?
The NHS defines healthy BMI as 18.5 to 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9. These lower thresholds reflect higher health risks in these populations at the same BMI level.
How do I calculate BMI if I use stone and pounds instead of kg?
Convert first: multiply your stone by 6.35 to get kg, or use our free weight converter. Then apply the standard formula: weight (kg) ÷ height (m)². Alternatively, use the imperial approximation: (weight in lbs × 703) ÷ height (inches)².
Is BMI accurate for everyone?
No. BMI doesn't account for muscle mass, so athletes may have high BMI despite low body fat. It's also less reliable for older adults, children, and pregnant women. Always discuss your personal BMI with your GP for context specific to your health.
What's the difference between overweight and obese BMI?
Overweight BMI ranges from 25.0 to 29.9, while obese starts at 30.0 and above. The NHS further divides obesity into three classes: I (30.0–34.9), II (35.0–39.9), and III/severe obesity (40.0+). Each category carries different health risks.
Can I use the BMI calculator instead of doing the maths myself?
Yes—our free BMI calculator on this page calculates your result instantly once you enter your weight and height. It's faster and removes any calculation errors. The calculator displays your BMI, category, and healthy weight range for your height.
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.