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 18.0 Mean?
A BMI of 18.0 places you firmly in the healthy weight range according to NHS guidelines. This means your weight is appropriate for your height, and you have a lower risk of weight-related health conditions compared to those with higher BMI values. The healthy BMI range is 18.5 to 24.9, so at 18.0 you're just slightly below this threshold but still considered to be at a healthy weight. This is a positive indicator for your overall health and fitness.
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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.
BMI 18.0 in Context: The Healthy Range Explained
The BMI formula divides your weight in kilograms by your height in metres squared (kg ÷ m²). A BMI of 18.0 is well within the healthy BMI range of 18.5 to 24.9 according to NHS guidelines. However, it's worth noting that BMI categories can vary by ethnicity — adults of South Asian, Chinese, Black African, or Black Caribbean heritage have different thresholds, with a healthy range of 18.5 to 22.9.
- BMI 18.0: Healthy weight — lower risk of obesity-related diseases
- Below 18.5: Underweight — may indicate nutritional concerns
- 18.5–24.9: Healthy weight range — optimal for most adults
- 25.0+: Overweight or obese — increased health risks
Use our free BMI calculator above to check how your current weight compares and to monitor any changes over time.
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.
Important BMI Limitations and Complementary Measures
While BMI is a useful screening tool, it has significant limitations that you should understand. BMI does not distinguish between muscle and fat — athletes or those with high muscle mass may have a higher BMI despite low body fat. It also doesn't account for where fat is stored, which matters for health risk. Waist circumference is equally important: for men, over 94cm (37 inches) indicates increased risk, while for women over 80cm (31.5 inches) is concerning.
For a complete health picture, consider pairing your BMI with our free weight converter to track measurements in your preferred units, and discuss your individual health with your GP if you have concerns.
- 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 18.0 considered underweight?
No. A BMI of 18.0 is in the healthy weight range (18.5–24.9). However, if your BMI were below 18.5, you would be classified as underweight. At 18.0, you're close to the lower boundary but still healthy. Monitor your nutrition and speak to your GP if you have concerns about your weight.
What weight corresponds to a BMI of 18.0?
This depends entirely on your height. For example, at 170cm (5ft 7in), a BMI of 18.0 equals approximately 52kg (8st 2lbs). At 175cm (5ft 9in), it's about 55kg (8st 8lbs). Use our free BMI calculator above to find your exact healthy weight range for your height.
Should I try to gain weight if my BMI is 18.0?
No. A BMI of 18.0 is healthy and you should not need to gain weight. However, if you feel unwell, fatigued, or are losing weight unintentionally, speak to your GP. Individual health depends on many factors beyond BMI alone.
How does BMI 18.0 compare to the average UK adult?
The average UK adult has a BMI of approximately 27.4, which falls in the overweight range. At 18.0, your BMI is significantly lower and in the healthy category. This suggests you're maintaining good weight management compared to the broader population.
Can I rely on BMI 18.0 as my only health measure?
BMI is useful but incomplete. It doesn't account for muscle mass, fitness level, or fat distribution. Consider additional measures like waist circumference, fitness level, and blood pressure. Your GP can provide personalised health advice based on your complete health picture, not just BMI.
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.