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
Is 17.9 kg a Healthy Weight?
17.9 kg converts to 2 stone 12 pounds in UK measurements. Whether this weight is healthy depends entirely on your height, age, and body composition. A weight that's healthy for a 4ft tall person would be underweight for someone 5ft 6in tall. This guide explains healthy weight ranges using NHS guidelines, shows you how to calculate your personal BMI using our free BMI calculator, and helps you understand what your weight 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.
Healthy Weight Ranges by Height
At 17.9 kg, you're in the very low weight category. To determine if this is healthy for you, compare your weight to the healthy range for your height according to NHS guidelines. The healthy BMI range is 18.5 to 24.9, which translates to specific weight ranges depending on height.
Example healthy weight ranges:
- At 4ft 6in (137 cm): healthy range is 32–43 kg (5st–6st 10lbs) — 17.9 kg is significantly below this
- At 5ft 0in (152 cm): healthy range is 43–56 kg (6st 11lbs–8st 12lbs) — 17.9 kg is significantly below this
- At 5ft 6in (168 cm): healthy range is 53–71 kg (8st 5lbs–11st 2lbs) — 17.9 kg is significantly below this
Use our free weight converter to check your exact weight in stone and pounds, then calculate your BMI using the BMI calculator on this page to see if your weight falls within a healthy range for your height.
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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.
What to Do If You're Underweight
If 17.9 kg is your actual weight and you're an adult, this is likely underweight according to NHS guidelines, regardless of height. Being underweight (BMI below 18.5) can affect bone density, immune function, and overall health. The first step is to speak with your GP, who can assess your individual health, check for any underlying causes, and provide personalised guidance.
Your GP may refer you to a specialist if needed. Increasing weight healthily involves eating nutrient-dense foods and building muscle through strength exercise, not just consuming extra calories. Keep track of your progress with our free progress tracker to monitor changes over time.
- 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 17.9 kg in stone and pounds?
17.9 kg converts to 2 stone 12 pounds (or 2st 12lbs) in UK measurements. To convert kilograms to stone, divide by 6.35. So 17.9 ÷ 6.35 = 2.82 stone. Our weight converter on this page can do this calculation instantly for any weight.
Is 17.9 kg healthy for an adult?
17.9 kg is significantly underweight for any adult, regardless of height. A healthy BMI for adults is 18.5 to 24.9. At this weight, you would have a BMI well below 18.5, which is classified as underweight. Speak with your GP to discuss your health and any underlying causes.
How do I know my healthy weight range?
Your healthy weight range depends on your height. The NHS BMI categories provide guidance: a BMI between 18.5 and 24.9 is healthy for most adults. Use the BMI calculator on this page with your height and weight to find your personal BMI, then check the healthy range for your height.
Should I be concerned about being underweight?
Yes, being underweight can affect bone health, immune function, and energy levels. If 17.9 kg is your current weight and you're an adult, speak with your GP. They can identify any underlying causes (illness, medication, malabsorption) and recommend safe ways to increase your weight through proper nutrition.
What's the difference between kg to stone conversion and healthy weight?
Conversion is simple maths — 17.9 kg = 2st 12lbs. Healthy weight is contextual and depends on your height, age, and health. The weight converter shows what kilograms equal in stone; the BMI calculator shows whether that weight is healthy for your specific height and body.
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.