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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Percentile Calculator For Height And Weight
A percentile calculator for height and weight helps assess how a child's growth compares to other children of the same age and sex. Unlike adult BMI, child growth is measured using age and sex-specific percentile charts rather than fixed categories. The NHS uses UK90 growth reference charts to track healthy development from birth through childhood, with percentiles indicating where a child falls relative to thousands of other children measured in growth studies. Understanding percentiles is essential for parents and healthcare professionals to identify any growth concerns early.
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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.
How Child Growth Percentiles Work In The UK
Child growth percentiles are not the same as adult weight categories. The UK90 growth reference charts are the standard used by the NHS and show how height and weight develop across childhood. A percentile tells you what percentage of children of the same age and sex are smaller than your child. For example, a child on the 50th percentile is right in the middle — half of their peers are taller and heavier, half are shorter and lighter.
- Below 2nd centile: significantly below average — discuss with your GP
- 2nd to 91st centile: healthy range for most children
- Above 91st centile: overweight — GP review recommended
- Above 98th centile: very overweight — GP assessment advised
Growth isn't linear — children grow in spurts. A single measurement doesn't tell the full story. Your GP tracks growth over time using centile charts, looking for consistent patterns rather than one-off measurements. Use our free BMI calculator to understand your own adult BMI, but remember that children require different assessment methods.
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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 Speak To Your GP About Your Child's Growth
Contact your GP if your child's growth crosses percentile lines significantly (e.g., drops from the 50th to the 10th percentile), grows much slower or faster than expected for their age, or shows signs of not developing typically. Your GP can plot measurements on the official UK90 charts and assess whether your child needs further evaluation. Most children within the 2nd to 91st percentile range are developing healthily, but individual growth patterns vary — some naturally small or large children remain healthy within wider ranges.
Your child will have regular growth checks at NHS health visitor appointments and during school nurse screenings. These professionals use the same percentile system and flag concerns early. If you're worried about your child's weight management as they get older, discuss healthy weight UK guidance with your GP rather than using adult weight loss approaches. Childhood is not the time for restrictive dieting — focus is on balanced nutrition and activity.
- 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's the difference between percentiles and BMI for children?
Percentiles compare a child's height and weight to other children their age and sex using UK90 growth charts. BMI categories used for adults (underweight, healthy, overweight, obese) don't apply to children because body composition changes dramatically during growth. Children's assessments look at growth trends over time, not fixed thresholds.
Is my child overweight if they're on a higher percentile?
Not necessarily. Being on a higher percentile (e.g., 75th) just means they're larger than average for their age — many large children are perfectly healthy. Your GP assesses overall health, not just percentile position. Growth rate and family history matter more than a single percentile number.
Can I use an adult BMI calculator for my child?
No. Adult BMI calculators are not appropriate for children under 18. The NHS provides specific growth assessment tools and centile charts for children. If you're concerned about your child's weight, your GP or health visitor will use the correct age and sex-specific charts to assess health.
How often should my child's growth be measured?
Growth checks are routine at health visitor appointments from birth to age 5, then at school entry and during school years. Your GP or health visitor will measure height and weight at these visits and plot them on UK90 charts. Between appointments, don't worry about frequent weighing — steady growth over months and years is what matters.
What if my child's growth percentile changes?
Small fluctuations are normal — children don't grow in straight lines. However, if growth consistently crosses percentile lines (e.g., drops from 50th to 10th or jumps from 25th to 91st) over time, mention it to your GP. They'll investigate whether there's an underlying cause or if it's normal variation.
Ready to take control of your weight loss journey?
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