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 Figure Out BMI Using the NHS Formula
BMI (body mass index) is a simple measurement that tells you whether your weight is healthy for your height. The NHS uses a standard BMI formula to assess weight categories across the UK population. Calculating your BMI takes just your height and weight — and understanding what your result means is an important first step in managing your health. Use our free BMI calculator above to find your BMI instantly, or read on to learn how the calculation works and what NHS guidance recommends for healthy weight ranges.
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 How to Calculate It
The BMI formula is straightforward: divide your weight in kilograms by your height in metres, squared. In other words: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your calculation would be 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI.
The NHS recommends using metric measurements (kg and metres) for accuracy, though you can also use imperial units if you prefer. If you're more familiar with stone and pounds, convert your weight to kilograms using our free weight converter first — this ensures precision in your calculation.
One important note: the BMI formula does not distinguish between muscle and fat. Athletes or very muscular individuals may have a higher BMI but lower body fat percentage, so BMI is a screening tool rather than a complete picture of 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 BMI Categories and What They Mean
According to NHS guidance, the standard BMI categories UK 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 and above).
However, the NHS also recognises that people from South Asian, Chinese, Black African, and Black Caribbean backgrounds face higher health risks at lower BMI levels. For these groups, the healthy BMI range is 18.5–22.9, and overweight begins at 23.0. If you belong to one of these ethnic groups, discuss your personal BMI targets with your GP to ensure guidance is tailored to your risk profile.
- 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 considered a healthy BMI according to the NHS?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9 due to higher cardiovascular and diabetes risk at lower BMI levels. Your GP can advise on your personal healthy weight range.
How do I convert my weight to kilograms if I'm in stone and pounds?
One stone equals 6.35 kilograms. Multiply your stone by 6.35, then add your pounds multiplied by 0.454. For example, 11 stone 7 pounds = (11 × 6.35) + (7 × 0.454) = 72.1 kg. Use our weight converter tool above for instant conversion between kg, stone, and pounds.
What are the limitations of BMI?
BMI does not account for muscle mass, bone density, or where fat is stored. Athletes may have high BMI but low body fat. BMI is also less accurate for elderly people, pregnant women, and those with significant muscle development. Use BMI as a screening tool alongside waist measurement and your GP's assessment.
When should I contact my GP about my BMI?
Contact your GP if your BMI is above 30, or above 27.5 if you have weight-related health conditions like high blood pressure, type 2 diabetes, or sleep apnoea. Your GP can assess your individual health and discuss weight management options, including referral to NHS tier 3 weight management services if appropriate.
How is BMI used in NHS weight management services?
The NHS uses BMI as one assessment tool within tier 3 specialist weight management services. Eligibility typically requires BMI ≥30, or ≥27 with weight-related comorbidities. If approved, the NHS offers behaviour change programmes, dietary support, and in some cases, prescription weight loss medications alongside lifestyle changes.
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.