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
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Height Percentile Boy Calculator — UK Guide
Understanding your boy's height percentile helps you track whether his growth is healthy and typical for his age. In the UK, the NHS uses growth reference charts based on the UK90 centile system to monitor children's development from birth through to 18 years old. Height percentiles compare a child's height to age-matched peers — for example, the 50th percentile means a boy is taller than 50% of children his age. This guide explains what percentiles mean, how to use NHS growth charts, and when to discuss growth concerns with your GP.
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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.
Understanding Height Percentiles and UK Growth Charts
Height percentiles indicate where a child ranks compared to other children of the same age and sex. The NHS uses the UK90 growth reference charts, which are based on measurements of UK children and are updated regularly to reflect modern growth patterns. A boy at the 75th percentile is taller than 75% of boys his age; a boy at the 25th percentile is taller than 25% of his peers.
- 50th percentile: Average height for age — the median
- Above 97th percentile: Exceptionally tall — may indicate rapid growth or other factors
- Below 3rd percentile: Notably short — warrants GP discussion
The UK90 charts account for natural variation in growth patterns. Most healthy children track along one centile line throughout childhood. A sudden shift upward or downward, or crossing multiple centile lines, may indicate something worth discussing with your GP. Growth is influenced by genetics, nutrition, physical activity, sleep, and overall health.
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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.
When to Seek GP Advice About Your Son's Height
Contact your GP if your son's height growth seems to slow, he crosses centile lines unexpectedly, or you have concerns about his development. Growth faltering — where a child's growth rate declines — can sometimes signal underlying health issues including thyroid problems, coeliac disease, or nutritional deficiencies. Your GP can plot your son's measurements on NHS growth charts, review growth trends over time, and refer to a paediatrician if needed. Routine NHS health checks include height and weight measurement. The UK health guide emphasises that healthy growth is individual — some variation is completely normal and doesn't always indicate a problem.
- 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 does the 50th percentile mean for my boy's height?
The 50th percentile is the median or average height for boys of that age. A boy at this percentile is taller than 50% of boys his age and shorter than 50%. It represents typical, healthy growth — not tall or short, just average.
Should I be concerned if my son is below the 25th percentile?
Not necessarily. Children naturally vary in height due to genetics, ethnicity, and family patterns. If he's tracking steadily along a consistent centile line and is healthy, this is normal. Discuss concerns with your GP if growth seems to slow or if he crosses centile lines unexpectedly.
How do UK90 growth charts differ from other growth charts?
The UK90 charts are based on measurements of UK children and reflect modern growth patterns. They're specifically designed for use in the UK and are more representative of current UK child populations than older international standards.
At what age should I stop tracking height percentiles?
Height tracking is standard through childhood and adolescence. Most boys complete their growth by late teens (around age 18). NHS health services monitor growth throughout childhood, and height is recorded at school health checks and GP appointments.
Can I use a height percentile calculator at home?
Yes — you can use growth reference charts or online calculators once you know your son's precise height and age. However, NHS health professionals use calibrated equipment and plotting on official UK90 charts for accuracy. Your GP or health visitor can give you the most reliable assessment.
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.