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 Is The Perfect BMI?
There's no single "perfect" BMI because health varies from person to person, but the NHS defines a healthy BMI range as 18.5 to 24.9 for most UK adults. Your perfect BMI depends on your age, ethnicity, muscle mass, and overall health — not just a number on a chart. Understanding what your BMI means and how to calculate it is the first step towards managing your weight effectively. Use our free BMI calculator above to check where you fall within the healthy range, and discover what those numbers actually mean 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.
NHS BMI Categories and Healthy Ranges
The NHS BMI formula is straightforward: weight (kg) divided by height (m) squared. According to NHS BMI guidelines, here's how UK adults are classified:
- Below 18.5 = Underweight
- 18.5–24.9 = Healthy weight (the ideal bmi range uk)
- 25.0–29.9 = Overweight
- 30.0–34.9 = Obese (Class I)
- 35.0–39.9 = Obese (Class II)
- 40.0+ = Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the overweight bmi threshold is lower — the healthy range starts at 18.5 but ends at 22.9, and overweight begins at 23.0. This reflects higher cardiovascular risk in these populations at lower BMI levels. The healthy bmi concept isn't one-size-fits-all; ethnicity genuinely matters for health assessment. You can calculate your personal BMI using our weight converter and BMI calculator above to see exactly where you sit.
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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.
BMI Limitations and What "Perfect" Really Means
The term "perfect BMI" can be misleading because BMI limitations are significant. BMI doesn't distinguish between muscle and fat — athletes often have high BMI but low body fat. It also ignores where fat is stored; excess weight around the waist is riskier than weight distributed elsewhere. Age, bone density, pregnancy, and medical conditions all affect what's truly healthy for you. Rather than chasing a perfect number, focus on the healthy range (18.5–24.9) and use complementary measures: waist circumference matters (under 94cm for men, under 80cm for women indicates lower risk). Your GP can give personalised advice about what's genuinely perfect for your individual health profile, considering factors a bmi calculator alone cannot assess.
- 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 BMI number is considered perfect?
The NHS considers a BMI between 18.5 and 24.9 to be healthy weight for most UK adults. Within this range, any number is considered "perfect" — there's no single ideal figure. For South Asian, Chinese, Black African, or Black Caribbean adults, the healthy range is 18.5–22.9. Health is about being within the range for your ethnicity, not hitting one specific number.
Is a BMI of 22 perfect?
A BMI of 22 falls comfortably within the healthy range (18.5–24.9) for most UK adults, and would be considered ideal. However, "perfect" depends on your individual circumstances — muscle mass, age, medical history, and family genetics all matter. Use our BMI calculator to see where your personal BMI sits and discuss any health concerns with your GP.
Why don't I have a perfect BMI even though I feel healthy?
You might feel healthy outside the "perfect" range due to high muscle mass, good cardiovascular fitness, or other factors BMI doesn't measure. BMI is a screening tool, not a complete health assessment. Waist circumference, fitness level, blood pressure, and blood sugar are also important. Your GP can help determine if your actual health matches your BMI reading.
What's the difference between healthy BMI and perfect BMI?
There's no meaningful difference — "healthy BMI" and "perfect BMI" both refer to the NHS range of 18.5–24.9. Some people use "perfect" informally, but the NHS uses "healthy weight" as the official term. Any BMI within the healthy range is considered appropriate for health purposes. Individual variation is normal and healthy.
Can my perfect BMI be different from the NHS range?
Your perfect BMI should fall within the NHS healthy range (18.5–24.9), but what's optimal within that range varies individually based on muscle mass, genetics, and health conditions. A GP or registered dietitian can help you identify your personal ideal weight considering your unique circumstances, rather than relying on BMI alone. Always consult a healthcare professional for personalised guidance.
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.