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 BMI for Adults?
BMI (Body Mass Index) is a health screening tool that measures the relationship between your weight and height. In the UK, the NHS uses BMI to help assess whether an adult's weight falls within a healthy range. BMI is calculated by dividing your weight in kilograms by your height in metres squared. It's a useful starting point for understanding your weight health, though it has important limitations you should know about. Use our free BMI calculator above to find your personal BMI instantly and see where it falls on the NHS scale.
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 & Healthy Weight Ranges
The NHS recognises four main BMI categories for adults:
- Healthy weight: BMI 18.5–24.9 — Associated with lower health risks
- Overweight: BMI 25.0–29.9 — Increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0–34.9 — Moderate health risk
- Obese (Class II): BMI 35.0–39.9 — Higher health risk
- Severely obese (Class III): BMI 40.0+ — Significant health risk
These NHS BMI ranges apply to most UK adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher health risks at lower weights. Your GP can discuss what your individual BMI means for your health and whether any action is recommended.
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.
NHS Weight Management Support & When to Seek Help
If your BMI falls outside the healthy range, the NHS offers support through its weight management pathway. Start by speaking to your GP, who can assess your overall health and discuss whether weight management support would help. The NHS provides tier 1 support through self-help resources and digital tools like our free BMI calculator and weight converter. If needed, your GP can refer you to a tier 2 or tier 3 specialist weight management service in your area. These services offer behaviour change programmes, dietary advice, and—in some cases—prescription weight loss medication. Remember that BMI is just one health marker; your GP will consider your overall health, family history, and any existing conditions when advising you.
- 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 healthy BMI range according to the NHS?
The NHS defines a healthy BMI for most UK adults as 18.5–24.9. This range is associated with lower health risks. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower healthy range of 18.5–22.9 due to higher disease risk at higher BMIs.
How do I calculate my BMI?
BMI is calculated by dividing your weight in kilograms by your height in metres squared (BMI = kg ÷ m²). For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 22.9. Use our free BMI calculator on this page to calculate yours instantly.
What are the limitations of BMI?
BMI does not distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. It also doesn't account for where fat is stored (waist measurement matters too), age-related muscle loss, or individual variations in bone density. Your GP can assess your health beyond BMI alone.
Should I be concerned if my BMI is overweight?
A BMI in the overweight range (25.0–29.9) doesn't automatically mean you need treatment, but it's worth discussing with your GP. Small lifestyle changes like increased activity or modest dietary adjustments can help. Your GP will consider your overall health, family history, and any existing conditions before recommending action.
How can I use the NHS weight management pathway?
Start by booking a GP appointment to discuss your weight and health. Your GP can provide initial support and—if appropriate—refer you to specialist tier 2 or tier 3 weight management services in your area. These services offer behaviour change programmes, dietary support, and sometimes prescription medication alongside lifestyle changes.
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.