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
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What's Your Ideal Weight? Understanding BMI and Healthy Ranges
Your ideal weight isn't a single number — it's a range that depends on your height, age, and individual health. The NHS uses BMI (body mass index) as the primary screening tool to determine healthy weight ranges for UK adults. Using the standard BMI formula and NHS guidelines, a healthy BMI sits between 18.5 and 24.9. However, your ideal weight also depends on factors like muscle mass, bone density, and where fat is stored on your body. Our free BMI calculator above can help you find your personal healthy weight range instantly. This guide explains how the NHS defines ideal weight, what the BMI categories mean, and when to seek support from your GP.
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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 Healthy Weight Ranges
The NHS defines ideal weight using BMI categories that apply to all UK adults aged 18 and over. According to NHS guidance, a healthy BMI ranges from 18.5 to 24.9, which represents the weight range associated with the lowest health risk.
- Underweight: BMI below 18.5 — may indicate insufficient nutrition
- Healthy weight: BMI 18.5–24.9 — associated with best health outcomes
- Overweight: BMI 25.0–29.9 — increased health risks begin to emerge
- Obese (Class I): BMI 30.0–34.9 — moderate health risks
- Obese (Class II): BMI 35.0–39.9 — higher health risks
- Severely obese (Class III): BMI 40.0 and above — significant health risks
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: healthy weight is BMI 18.5–22.9, and overweight begins at BMI 23.0. This is because these populations face higher diabetes and cardiovascular disease risk at lower BMI levels. Use our free BMI calculator on this page to find exactly where your BMI falls and what category applies to you.
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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.
NHS Weight Management Pathway and When to Seek Help
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway to support you. This begins with Tier 1 self-help — using free digital tools, NHS weight loss plans, and community programmes. Your GP can refer you to Tier 2 primary care services for behaviour change support and advice. For those with a BMI over 30 (or 27.5 with weight-related health conditions), Tier 3 specialist services may be available, where prescription weight loss medications like Mounjaro or Wegovy can be considered alongside lifestyle changes. Tier 4 bariatric surgery is available for severe obesity with significant health complications. Remember: even losing 5–10% of your body weight can meaningfully improve your health, blood pressure, and blood sugar control. Your GP can discuss which support is right for 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's the difference between my ideal weight and BMI range?
Your "ideal weight" is any weight within the healthy BMI range for your height — typically a range of 10–15 kg rather than a single number. BMI range is the tool the NHS uses to calculate this. For example, at 5ft 8in (173cm), the healthy BMI range is approximately 55–74 kg. Your ideal weight within that range depends on factors like muscle mass, bone structure, and personal health goals. Your GP can help identify your personal target.
Does the BMI formula work the same for everyone?
The BMI formula is the same for all adults, but interpretation differs. The NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher metabolic disease risk. BMI also has limitations — it doesn't distinguish muscle from fat, so very muscular individuals may have high BMI despite low body fat. Your GP can assess whether BMI alone is appropriate for your health picture.
How do I calculate my ideal weight range using BMI?
To calculate your healthy weight range, use this formula: multiply 18.5 by your height in metres squared (for the lower bound), and 24.9 by the same figure (for the upper bound). For example, at 1.73m: lower bound = 18.5 × (1.73)² = 55.4 kg; upper bound = 24.9 × (1.73)² = 74.5 kg. Our free BMI calculator above does this instantly for you.
Should I aim for the low or high end of the healthy BMI range?
The entire healthy BMI range (18.5–24.9) is associated with good health outcomes. Where you aim within that range depends on your age, fitness level, muscle mass, and personal goals. A weight at the higher end may be appropriate if you're muscular or older; the lower end if you're younger or focus on cardiovascular health. Your GP or a registered dietitian can advise on a target that's right for you.
What if I have a medical condition — does my ideal weight change?
Yes. Certain conditions like type 2 diabetes, polycystic ovary syndrome (PCOS), or thyroid disorders may affect your ideal weight range or the rate at which you should aim to lose weight. Additionally, some medications affect weight. Always discuss your ideal weight target with your GP, who can factor in your personal health history and recommend safe, sustainable approaches tailored to your situation.
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.