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
How BMI Relates to Weight Loss
BMI (body mass index) is a key health measure used to assess whether your weight is healthy for your height. If you're carrying excess weight, losing even 5–10% of your body weight can improve your BMI category and reduce health risks. The NHS recommends losing weight at a sustainable rate of 0.5 to 1 kg per week alongside lifestyle changes. Use our free BMI calculator above to check your current BMI and see what a healthy range looks like for your height, then track your progress as you work towards your goals.
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.
BMI Categories and Weight Loss Targets
The BMI formula is weight (kg) divided by height (m) squared. According to NHS BMI categories UK, a healthy BMI falls between 18.5 and 24.9. If your BMI is 25–29.9, you're classified as overweight; 30–34.9 is obese class I; 35–39.9 is obese class II; and 40 or above is severely obese.
To reach a healthy BMI through weight loss, calculate your target weight using the BMI range UK for your height. For example, if you're 1.75m tall, a healthy weight range is approximately 55–76 kg. The overweight BMI threshold of 25 means losing even 2–3 kg can shift you from overweight into the healthy category. Use our weight converter and BMI calculator above to determine your personalised target range and monitor your progress with measurable, realistic goals.
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.
BMI Limitations and Complementary Measures
While BMI is a useful screening tool, it has significant BMI limitations. BMI doesn't distinguish between muscle and fat — a very muscular person may have a high BMI but low body fat. It also doesn't account for where fat is stored around your body. The NHS recommends combining BMI assessment with waist circumference measurements: men over 94 cm (37 inches) face increased cardiovascular risk; women over 80 cm (31.5 inches) face similar risk. For a more complete picture of your health, consider body composition analysis and discuss your weight loss strategy with your GP, especially if you have existing health conditions.
- 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 a healthy BMI for weight loss?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9. If your BMI is above 25, weight loss can help you reach this range. The amount of weight you need to lose depends on your height and current weight — use our BMI calculator to determine your personalised target range.
How much weight loss changes your BMI category?
Small weight changes can shift your BMI category. For example, losing 3 kg might move you from overweight (25–29.9) into the healthy range (18.5–24.9), depending on your height. Each kilogram lost typically reduces your BMI by 0.1–0.15 points.
Is BMI the only measure for weight loss success?
No. While BMI is useful, it doesn't account for muscle mass or fat distribution. The NHS recommends also measuring waist circumference and considering overall health improvements like better blood pressure, improved energy, and reduced joint pain — not just the number on the scale.
Why do ethnicity-adjusted BMI thresholds exist?
People of South Asian, Chinese, Black African, and Black Caribbean heritage face higher health risks at lower BMI levels. The NHS recommends lower thresholds for these groups: a healthy BMI starts at 18.5 but "healthy weight" for some groups is 18.5–22.9 instead of 18.5–24.9.
Can weight loss medication help me reach a healthy BMI?
For eligible adults, prescription weight loss medications like GLP-1 injections may support weight loss alongside diet and exercise. These require a clinical assessment and prescription from a healthcare professional. Our GLP-1 weight loss calculator can help you estimate potential progress with medication.
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.