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 a BMI Indicator Calculator?
A BMI indicator calculator uses the BMI formula to show you where your weight falls on the NHS health scale. It tells you instantly whether your weight is in the healthy, overweight, or obese range for your height. The calculation is straightforward, but understanding what your result means is key to making informed health decisions. Our free BMI calculator above gives you your personal BMI and explains which category you fall into according to NHS guidelines.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 the BMI Formula Works and What the Ranges Mean
The BMI formula is simple: weight (kg) divided by height (metres) squared. For example, if you weigh 75kg and are 1.75m tall, your BMI is 75 ÷ (1.75)² = 24.5, which falls in the healthy weight range.
According to NHS BMI categories UK, the standard ranges are:
- Below 18.5 = Underweight
- 18.5–24.9 = Healthy weight
- 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)
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: a healthy range of 18.5–22.9 applies to you, and the overweight BMI threshold begins at 23.0 due to higher health risks at lower BMI levels in these populations.
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.
Understanding BMI Limitations and What Else Matters
BMI limitations are important to understand. BMI does not distinguish between muscle and fat—athletes may have a high BMI but low body fat. It also ignores where fat is stored; carrying excess weight around your stomach carries greater health risk than weight distributed elsewhere. BMI is less accurate for elderly adults, during pregnancy, and in very muscular individuals.
Alongside your BMI, measure your waist circumference: over 94cm (men) or 80cm (women) indicates increased health risk. Your GP can provide personalised interpretation of your BMI and recommend lifestyle changes or treatment options tailored to your individual health profile.
- 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 BMI indicator and actual body fat percentage?
BMI is a simple weight-to-height ratio that screens health risk. Body fat percentage directly measures the proportion of fat in your body. BMI is quick and free to calculate but doesn't distinguish muscle from fat. Body fat percentage is more accurate but requires specialised equipment. Both are useful: use our BMI calculator as a starting point, then discuss results with your GP.
Can I use the BMI indicator calculator if I'm very muscular or athletic?
BMI may overestimate health risk if you're very muscular, as muscle is denser than fat. If you're an athlete or regularly strength train, discuss your BMI result with your GP. They can assess your actual body composition, measure your waist circumference, and evaluate your cardiovascular health to give you a complete picture beyond the BMI number.
Does the BMI indicator work the same for children?
No. Children's BMI is assessed differently using age and sex-specific growth charts (UK90 centile charts), not adult categories. If you're checking your child's weight, use the NHS Healthy Weight Calculator for children or ask your GP. Adult BMI categories do not apply to young people under 18.
How often should I check my BMI using the indicator calculator?
Check your BMI monthly or quarterly if you're actively working on weight management. More frequent checks (weekly) can be misleading due to normal fluid and food fluctuations. Track your progress over weeks and months rather than days. Our free progress tracker helps you log weight changes and see trends over time—use that alongside the BMI calculator.
If my BMI indicator shows I'm overweight, does that mean I need medication?
Not necessarily. The NHS recommends starting with lifestyle changes: a balanced diet with a calorie deficit of about 500 kcal/day and increased physical activity can achieve sustainable weight loss of 0.5–1kg per week. If lifestyle changes alone aren't sufficient after several months, your GP can discuss prescription options or referral to specialist weight management services, depending on your health profile.
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.