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 12.3 Kg a Healthy Weight?
12.3 kg converts to approximately 27.1 lbs in imperial measurements. Whether this weight is healthy depends entirely on your height — it's not possible to say if a weight is healthy without knowing your height. A person who is 150cm (4ft 11in) tall would have a different BMI at 12.3kg than someone who is 180cm (5ft 11in) tall. Use our free BMI calculator above to find your personal BMI instantly, or refer to the healthy weight ranges below to see where you fall for your height.
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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
To determine if 12.3kg is healthy for you, use the NHS BMI categories. A BMI between 18.5 and 24.9 is considered healthy weight for most UK adults. Here's how 12.3kg compares at different heights:
- At 150cm (4ft 11in): 12.3kg gives a BMI of 5.5 — this would be severely underweight and requires medical attention
- At 165cm (5ft 5in): 12.3kg gives a BMI of 4.5 — again, dangerously underweight
- At 180cm (5ft 11in): 12.3kg gives a BMI of 3.8 — severely underweight and medically concerning
In practice, 12.3kg is an extremely low weight for any adult and would indicate a serious health issue requiring urgent GP assessment. If you're tracking weight loss or managing a health condition, use our weight converter and BMI calculator to monitor your progress safely within healthy ranges.
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.
What To Do If Your Weight Is Outside The Healthy Range
If your BMI falls outside the healthy 18.5–24.9 range, it's important to speak with your GP. They can assess your individual health, discuss any underlying causes, and recommend appropriate support. Being significantly underweight (BMI below 18.5) can weaken your immune system, affect bone density, and cause other health problems.
The NHS offers free weight management support through your GP surgery. Your GP can refer you to tier 2 or tier 3 services for specialist guidance tailored to your needs. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply — ask your GP about ethnicity-adjusted guidance. Track your weight journey using our free progress tracker to monitor changes over time and share data with your healthcare team.
- 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.
How do I convert 12.3 kg to lbs?
Multiply 12.3 by 2.20462. The result is 27.1 lbs. Our free weight converter above will do this instantly — you can also convert between kg, stone, and lbs at the same time.
Is 12.3 kg a healthy weight for an adult?
12.3kg is severely underweight for any adult, regardless of height. This weight would indicate malnutrition or a serious underlying health condition. If you weigh this much or are concerned about being underweight, speak with your GP immediately.
What is the healthy weight range for my height?
Healthy weight depends on your height and sex. Use our BMI calculator above to find your healthy range instantly. For most UK adults, a BMI between 18.5 and 24.9 is healthy. Your GP can also provide personalised guidance based on your individual health.
Why is 12.3kg so underweight?
12.3kg is below the typical weight of a healthy newborn. Adult humans require significantly more body mass to maintain vital functions like body temperature, immune function, and bone density. Severe underweight can cause serious health complications.
Where can I get support if I'm underweight?
Contact your GP — they can assess the cause (malnutrition, illness, or other factors) and refer you to appropriate support. The NHS offers weight management services, nutritional counselling, and specialist care through the NHS tier system.
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.