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 counter and how do you use it?
A BMI counter is a simple tool that calculates your Body Mass Index — a measure of body fat based on your height and weight. It helps you understand whether your weight falls into a healthy range according to NHS guidelines. Using a BMI counter takes just seconds: enter your height and weight, and it instantly shows you your BMI number and which category you fall into. This quick assessment is the first step many people take when thinking about their health and weight management. Our free BMI calculator above will give you your result immediately in UK measurements.
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 BMI categories work and what the NHS recommends
The BMI formula divides your weight in kilograms by your height in metres squared (kg ÷ m²). The result places you in one of the NHS BMI categories:
- 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)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — a healthy BMI range of 18.5–22.9 applies, as these groups face higher health risks at standard BMI levels. The overweight BMI threshold starts at 23 for these populations. Use our free weight converter to check your weight in different units, then calculate your personal BMI using the counter on this page.
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.
Important limitations and complementary health measures
While a BMI counter is useful for screening, it has real limitations. BMI doesn't distinguish between muscle and fat — an athlete with high muscle mass may have a high BMI but low body fat. It also doesn't account for where fat is stored (belly fat carries greater health risk) or changes with age and hormones. The BMI limitations mean you shouldn't rely on it alone.
For a fuller health picture, also consider your waist circumference: men should aim for under 94cm (37 inches), women under 80cm (31.5 inches). Combine BMI assessment with regular physical activity, a balanced diet, and conversations with your GP. These factors together give a much better sense of your actual health than any single number.
- 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 and body fat percentage?
BMI is a simple height-to-weight ratio, whilst body fat percentage measures the actual amount of fat in your body. BMI doesn't distinguish between muscle and fat, so a muscular person may have a high BMI but low body fat. Body fat percentage is more precise but requires specialist equipment to measure accurately. Use BMI as a starting point, then discuss body composition with your GP if needed.
Can I use a BMI counter if I'm pregnant?
Standard BMI calculations aren't reliable during pregnancy because weight gain is expected and necessary. Your GP will monitor your weight and health using pregnancy-specific guidelines instead. Always discuss your weight and health with your antenatal care team rather than relying on a BMI counter during this time.
Is BMI accurate for older adults?
BMI becomes less accurate with age because older adults naturally lose muscle mass whilst body fat may increase. This means an older person's BMI might not reflect their actual health risk. Your GP can provide age-appropriate guidance on healthy weight ranges and fitness rather than using BMI alone as the sole measure.
What should I do if my BMI counter shows I'm overweight?
First, remember that BMI is one screening tool only — it doesn't diagnose any condition. If your result shows you're overweight, consider speaking with your GP about your health goals. Small, sustainable changes to diet and physical activity can help. Our free progress tracker can help you log changes over time, and your GP can discuss whether any support or treatment options might suit you.
How often should I check my BMI counter?
Checking your BMI monthly or every few months is reasonable if you're tracking weight changes. However, weight naturally fluctuates day-to-day due to hydration, hormones, and digestion — don't obsess over daily changes. Focus on longer-term trends. Our free progress tracker lets you log weights over weeks and months to see meaningful patterns rather than individual fluctuations.
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.