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
Understanding the Obesity Scale and Your BMI Category
The obesity scale, defined by the NHS, helps determine whether you're at a healthy weight or carrying excess weight that may affect your health. Your BMI (body mass index) is the key measurement used in this classification. If you're concerned about whether you're overweight or obese, our free BMI calculator above can give you an instant answer based on your height and weight. In the UK, being overweight is defined as a BMI between 25 and 29.9, while obesity begins at a BMI of 30 or higher. Understanding where you fall on this scale is the first step towards making informed health decisions with your GP.
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.
NHS BMI Categories and Obesity Thresholds
The NHS overweight threshold officially starts at a BMI of 25.0. Here are the full NHS BMI categories:
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Obese (Class II): BMI 35.0–39.9
- Severely obese (Class III): BMI 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds, with overweight starting at BMI 23.0 and obesity at 27.5 — because these groups have higher health risks at lower BMI levels. Use our free BMI calculator on this page to find your exact category instantly. Your GP can discuss what this means for your individual health.
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.
Waist Measurement and What to Do Next
While BMI is useful, waist circumference is equally important. The NHS recommends checking where you carry fat: a waist measurement over 94cm (37 inches) for men or 80cm (31.5 inches) for women indicates increased health risk, even at a lower BMI. This is because fat stored around the stomach poses greater cardiovascular risks than fat stored elsewhere. If your BMI falls in the overweight or obese BMI UK categories, the next step is to book an appointment with your GP. They can assess your overall health, discuss any weight-related conditions you may have, and help you create a personalised plan. This might include lifestyle changes, referral to NHS weight management services, or assessment for prescription weight loss support.
- 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 is the obesity scale and how does it work?
The obesity scale is an NHS framework using BMI (body mass index) to categorise adults into weight ranges: healthy weight (BMI 18.5–24.9), overweight (25.0–29.9), and obese categories starting at 30.0. BMI is calculated by dividing your weight in kg by your height in metres squared. Our free BMI calculator computes this instantly.
Am I overweight if my BMI is 27?
Yes — a BMI of 27 falls in the NHS overweight category (25.0–29.9). At this level, the NHS recommends lifestyle changes including balanced diet and physical activity. Your GP can assess whether any additional support is needed based on your overall health.
What's the difference between overweight and obese on the NHS scale?
Overweight is BMI 25.0–29.9; obesity starts at BMI 30.0. At the obese threshold, health risks including type 2 diabetes, cardiovascular disease, and joint problems increase significantly. Your GP can discuss personalised management options.
Does waist measurement matter if my BMI is healthy?
Yes — waist circumference is an independent health indicator. Even at a healthy BMI, a large waist (over 94cm for men, 80cm for women) signals increased risk. Measuring your waist complements your BMI check for a fuller health picture.
What should I do if I'm in the obese category?
Book an appointment with your GP to discuss your health. They can assess weight-related conditions, refer you to NHS weight management services, or discuss prescription weight loss options if appropriate. Use our progress tracker to monitor any changes you make.
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.