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 Should Your BMI Be? NHS Guidelines Explained
Your BMI (body mass index) should ideally fall between 18.5 and 24.9 according to NHS guidelines, which defines this range as a healthy weight for adults. However, the right BMI for you depends on your age, ethnicity, and overall health — not just a single number. The NHS BMI formula uses your weight and height to give a simple screening tool, though it has important limitations. This guide explains what NHS recommends, how to check your own BMI using our free calculator, and what it actually means for your health.
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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 and Healthy Weight Targets
The NHS uses these standard BMI categories for adults:
- Below 18.5 — Underweight
- 18.5 to 24.9 — Healthy weight (this is where NHS recommends you should aim)
- 25.0 to 29.9 — Overweight
- 30.0 to 34.9 — Obese (Class I)
- 35.0 to 39.9 — Obese (Class II)
- 40.0 and above — Severely obese (Class III)
These are the standard thresholds for most UK adults. However, if you are of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher health risks at the same BMI level. For these groups, a healthy BMI range is 18.5 to 22.9, and overweight begins at 23.0. You can calculate your personal BMI instantly using our free BMI calculator above to see where you fall on the NHS scale.
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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 and When to Seek Help
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway to help. Start with self-help resources through your GP, including the free NHS Weight Loss Plan and digital support tools. If you need more structured support, your GP can refer you to a tier 2 or tier 3 weight management service, where you'll receive personalised advice, behaviour change support, and potentially prescription weight loss medication if appropriate. The NHS emphasises that BMI is a screening tool, not a diagnosis — your GP will consider your overall health, waist circumference, and any weight-related conditions (like high blood pressure or type 2 diabetes) when deciding next steps. Use our weight converter to track your progress in whichever units feel familiar to you.
- 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 ideal BMI I should aim for?
According to NHS guidelines, the ideal BMI range for most UK adults is 18.5 to 24.9. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower range of 18.5 to 22.9 due to higher health risks at standard thresholds. Your GP can advise on what's right for your individual health.
Does my BMI need to be exactly in the healthy range?
No — BMI is a screening tool, not a precise health measure. It doesn't account for muscle mass, bone density, or where fat is stored on your body. Many athletes have higher BMI due to muscle, yet excellent health. Your GP considers BMI alongside waist measurement, fitness level, and medical history when assessing your health.
What if my BMI is outside the healthy range — should I worry?
Not necessarily a cause for panic, but it is a signal to discuss with your GP. Even modest weight loss of 5–10% can improve blood pressure, blood sugar control, and reduce health risks. Your GP can advise whether action is needed and what support is available through the NHS.
Can I use BMI to check if I'm overweight?
Yes — BMI is useful for screening. A BMI of 25.0 to 29.9 is classified as overweight by NHS standards. However, BMI doesn't tell the full story. Waist circumference and overall fitness matter too. Use our free BMI calculator to check yours, then discuss results with your GP for personalised guidance.
What should I do if my BMI shows I'm obese?
Contact your GP for a health assessment. The NHS offers weight management support including behaviour change programmes, digital tools, and in some cases, prescription medication or specialist services. Your GP will help create a personalised plan suited to your health needs and 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.