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 Weight Is Obese in the UK?
Obesity is defined by your BMI (body mass index) rather than a specific weight, because the same weight can be healthy or obese depending on your height. According to NHS guidelines, a BMI of 30 or above is classified as obese. Use our free BMI calculator above to check where you stand, and this guide will help you understand what the NHS considers obese and what it means for your health.
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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 Obesity Thresholds and BMI Categories
The NHS defines obesity as a BMI of 30 or above. However, there are three classes of obesity, each with different health implications:
- Class I obesity: BMI 30–34.9
- Class II obesity: BMI 35–39.9
- Severely obese (Class III): BMI 40 and above
Importantly, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — obesity may start at a BMI of 27.5 rather than 30, because these groups face higher health risks at lower BMI levels. The overweight category (BMI 25–29.9) comes before obesity, and a healthy weight range is a BMI of 18.5–24.9. Your exact weight at which you reach obesity depends entirely on your height — use our free BMI calculator to find your personal threshold.
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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.
Waist Measurement and Next Steps
Beyond BMI, waist measurement is also important — even at the same BMI, carrying excess weight around your stomach increases health risks. The NHS recommends checking if your waist circumference exceeds 94cm (37 inches) for men or 80cm (31.5 inches) for women, which signals increased health risk. If you've calculated that you're overweight or obese, the next step is to speak with your GP about your weight and health. Your GP can discuss safe, sustainable weight loss options — which may include lifestyle changes, dietary support, or in some cases, prescription weight loss medication following a full health assessment.
- 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 weight is obese for a woman 5ft 5in tall?
There's no single weight that defines obesity — it depends on your BMI. For a woman 5ft 5in (165cm) tall, a BMI of 30 (which marks the start of obesity) corresponds to approximately 73kg (11st 6lbs). However, calculate your own BMI using our free calculator above to be certain, as individual body composition varies.
Is BMI 30 definitely obese?
Yes, according to NHS guidelines, a BMI of 30 or above is classified as obese. However, BMI has limitations — it doesn't account for muscle mass. An athlete might have a high BMI but low body fat. Your GP can assess your individual health picture beyond BMI alone.
Does waist measurement matter if my BMI is healthy?
Yes. Even at a healthy BMI, excess weight concentrated around your stomach increases health risks. The NHS recommends checking both your BMI and waist circumference. A waist over 94cm (men) or 80cm (women) signals increased risk, even if your BMI is in the healthy range.
What should I do if I'm obese?
Speak to your GP. They can assess your individual health and discuss safe weight loss options — which might include dietary changes, exercise, NHS weight management programmes, or prescription weight loss medication if clinically appropriate. Losing even 5–10% of your body weight can have meaningful health benefits.
Are different ethnic groups considered obese at different weights?
Yes. The NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage — obesity may start at BMI 27.5 rather than 30, because these groups have higher health risks at lower BMI levels. Ask your GP if adjusted thresholds apply to you.
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.