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 Does a BMI of 18 Mean?
A BMI of 18 falls comfortably within the healthy weight range according to NHS guidelines. This means your weight is at a level associated with lower health risks for most adults. However, BMI is just one screening tool — it doesn't account for muscle mass, bone density, or where fat is stored. Your overall health depends on many factors including fitness, diet, sleep, and stress levels. If you want to check your personal BMI, use our free BMI calculator above to see where you stand and get your full health context.
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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 What They Mean
The NHS divides BMI into five main categories to help adults understand their weight health:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- Obese (Class I): BMI 30.0 to 34.9
- Obese (Class II): BMI 35.0 to 39.9
- Severely obese (Class III): BMI 40.0 and above
At BMI 18, you're in the healthy BMI range — the sweet spot according to NICE guidance. However, the NHS also recognises that BMI limitations exist. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply, as these groups face higher health risks at standard BMI levels. Use our weight converter to check your weight in different units, and remember that maintaining a healthy BMI alongside regular physical activity and a balanced diet supports long-term wellbeing.
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 and When to Seek Support
If you have a BMI of 18, you're unlikely to need weight loss support from the NHS. However, if your weight changes significantly or you have health concerns, speak to your GP. The NHS weight management pathway offers support at different levels: Tier 1 includes self-help tools and community programmes, Tier 2 involves primary care interventions, Tier 3 offers specialist multidisciplinary services with medication options, and Tier 4 covers bariatric surgery for severe obesity. Your GP can assess your individual health and recommend the right level of support if needed. Focus on maintaining your healthy weight through balanced nutrition, regular exercise, adequate sleep, and stress management.
- 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.
Is a BMI of 18 considered healthy?
Yes. According to NHS guidelines, a BMI of 18 falls within the healthy weight range of 18.5 to 24.9. This indicates your weight is at a level associated with lower health risks for most adults. However, health is multifactorial — fitness, diet, sleep quality, and stress levels also matter significantly.
What weight corresponds to a BMI of 18 at different heights?
BMI depends on both weight and height. For example, at 1.70m (5ft 7in), a BMI of 18 equals approximately 52kg (8st 3lbs). Use our free BMI calculator above to find your exact weight range for a BMI of 18 based on your height.
Should I try to lose weight if my BMI is 18?
No. A BMI of 18 is in the healthy range, so intentional weight loss is not recommended. Instead, focus on maintaining your current weight through balanced eating, regular physical activity, and good sleep. If you have specific health concerns, discuss them with your GP.
Why does the NHS have different BMI thresholds for different ethnic groups?
The NHS recognises that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher health risks at standard BMI levels. Lower thresholds (healthy range 18.5–22.9) for these groups reflect differences in body composition and disease risk. Your GP can explain what's appropriate for your individual circumstances.
Are there BMI limitations I should know about?
Yes. The BMI formula doesn't distinguish muscle from fat, so athletes or very muscular people may have high BMI but low body fat. BMI also doesn't account for age, bone density, or where fat is stored. Waist circumference is another useful health marker — discuss your overall health picture with your GP.
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.