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
What Is Chart 40 and What Does It Mean for Your Health?
Chart 40 typically refers to a BMI of 40 or above, which falls into the severely obese category according to NHS guidelines. This weight classification indicates an increased health risk and may qualify you for prescription weight management support. Understanding your weight status is the first step towards healthier outcomes. Our free BMI calculator can help you determine your exact BMI and health category instantly, whether your weight is measured in kg, stone, or pounds. Taking action early makes a meaningful difference to your long-term health and wellbeing.
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.
BMI 40 and NHS Health Classification
A BMI of 40 or above falls into the severely obese (Class III) category according to NHS guidelines. At this weight level, individuals face significantly elevated health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and sleep apnoea. The good news is that even modest weight loss of 5–10% of body weight can deliver meaningful health benefits. Under NHS weight management guidance, adults with a BMI of 40 or above are eligible for referral to specialist tier 3 weight management services, where prescription medications may be considered alongside lifestyle changes. Your GP can provide a personalised assessment and discuss the options available to you. Use our free weight converter to understand your weight in different units, then calculate your precise BMI using the calculator on this page.
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.
Weight Management Options for Chart 40
If you have a BMI of 40, several evidence-based pathways are available. The NHS recommends starting with tier 1 and tier 2 support, including behavioural programmes and digital tools like our GLP-1 weight loss calculator. For those who need additional support, prescription weight loss medications may be appropriate following clinical assessment through specialist services. These medications, including semaglutide (Wegovy) and tirzepatide (Mounjaro), are prescription-only and work alongside a reduced-calorie diet and physical activity. Access in the UK is through NHS specialist services or private prescribers. Track your progress over time using our free progress tracker, and remember that sustainable weight loss typically occurs at a rate of 0.5–1 kg per week.
- 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 health risks are associated with a BMI of 40?
A BMI of 40 significantly increases the risk of type 2 diabetes, heart disease, stroke, high blood pressure, sleep apnoea, and certain cancers. Even a 5–10% reduction in body weight can meaningfully improve these risk factors and your overall health outcomes.
Can I access prescription weight loss medication with a BMI of 40?
Yes. Adults with a BMI of 40 are typically eligible for NHS specialist weight management services, where prescription medications may be considered. Eligibility depends on individual health factors and regional availability. Your GP can refer you to these services.
What does Chart 40 mean exactly?
Chart 40 refers to a BMI of 40 or above, which falls into the severely obese category. This classification indicates a significantly elevated health risk according to NHS guidelines and qualifies for enhanced weight management support.
How much weight would I need to lose from a BMI of 40 to reach a healthy weight?
The amount varies by height and individual factors. Use our free BMI calculator above to check your healthy weight range. Generally, moving from BMI 40 to under 25 requires substantial weight loss, but starting with a 5–10% reduction delivers significant health benefits.
Are Wegovy and Mounjaro available through the NHS for BMI 40?
Both medications are prescription-only and may be available through NHS specialist weight management services, though regional availability varies. Private access is also available following clinical assessment with a UK-licensed prescriber. Individual eligibility is assessed based on your specific health circumstances.
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.