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
Check Your BMI Using NHS Guidelines
Checking your BMI is a quick way to understand whether your weight is in a healthy range according to NHS guidance. BMI (body mass index) is calculated from your height and weight, and the NHS uses it as a screening tool to identify health risks. Use our free BMI calculator above to find your personal BMI instantly, then compare it against the official NHS categories to see where you fall. Keep in mind that BMI has limitations — it doesn't account for muscle mass or where fat is stored — but it's a useful starting point for a conversation with your GP about your health.
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 Categories & What They Mean
The NHS uses standardised BMI categories to help adults understand their weight status. These are based on clinical evidence about health risks at different weight ranges:
- Underweight: BMI below 18.5 — may indicate insufficient weight for optimal health
- Healthy weight: BMI 18.5 to 24.9 — lowest risk of weight-related health conditions
- Overweight: BMI 25.0 to 29.9 — increased risk of type 2 diabetes and heart disease
- Obese (Class I): BMI 30.0 to 34.9 — significantly increased health risks
- Obese (Class II): BMI 35.0 to 39.9 — further increased risks
- Severely obese (Class III): BMI 40.0 and above — highest risk category
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds. A healthy BMI for these groups starts at 18.5 but overweight begins at 23.0, reflecting higher health risks at lower weights in these populations.
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 & When to Seek Help
The NHS offers a structured pathway for weight management support. If your BMI puts you at health risk, your GP can discuss lifestyle changes and potentially refer you to NHS weight management services. The NHS pathway includes tier 1 (self-help and community support), tier 2 (primary care programmes like the NHS Weight Loss Plan), tier 3 (specialist multidisciplinary weight management services), and tier 4 (bariatric surgery for severe obesity). Prescription weight loss medications are typically available through tier 3 specialist services for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes or high blood pressure. Waiting times and availability vary by region, so speak to your GP about what's available locally.
- 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.
How do I check my BMI using the NHS formula?
BMI is calculated by dividing your weight in kilograms by your height in metres squared (BMI = weight ÷ height²). Use our free BMI calculator on this page — simply enter your weight and height in either metric or imperial units and it will calculate your BMI instantly against NHS categories.
What BMI is considered healthy by the NHS?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9 for most UK adults. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, a healthy BMI is 18.5 to 22.9, as these groups face higher health risks at higher weights.
What should I do if my BMI is in the overweight or obese range?
If your BMI is 25 or above, discuss it with your GP. They can assess your overall health, identify any weight-related conditions, and discuss options including lifestyle changes, NHS weight management programmes, or specialist referrals. Even a 5–clinically studied weight loss can improve health markers.
Are there limitations to using BMI to check weight?
Yes — BMI doesn't distinguish between muscle and fat, so athletes may have high BMI but low body fat. It also doesn't account for where fat is stored (waist circumference matters) or individual circumstances like age or ethnicity adjustments. Use BMI as a screening tool alongside other health measures, not as a complete health picture.
Can I access weight loss medication through the NHS?
Yes, prescription weight loss medications are available through NHS tier 3 specialist weight management services. You'll typically need a GP referral and a BMI of 30 or above (or 27+ with weight-related health conditions). Availability, eligibility, and waiting times vary significantly by region — ask your GP about local services.
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.