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
BMI and Weight Loss Calculator — NHS Guidance for UK Adults
Understanding your BMI and weight loss options is the first step toward sustainable health. Our free BMI and weight loss calculator helps you see where you stand according to NHS guidelines, and what steps might be right for you. This guide explains the NHS approach to weight management, how BMI categories work in the UK, and when to speak with your GP about weight loss support.
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 What They Mean
The NHS uses a standardised BMI formula to categorise adult weight status. Your BMI is calculated by dividing your weight in kilograms by your height in metres squared. The resulting number falls into one of five categories that guide NHS health recommendations.
- Healthy weight: BMI 18.5–24.9 — associated with the lowest health risks
- Overweight: BMI 25.0–29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0–34.9 — higher health risks present
- Obese (Class II): BMI 35.0–39.9 — significantly elevated health risks
- Severely obese (Class III): BMI 40.0+ — very high health risk requiring medical support
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these groups face higher cardiovascular and metabolic risks at lower BMI levels. If this applies to you, discuss your personal BMI range with your GP.
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 Pathway and When to Seek Help
The NHS offers a structured approach to weight management across four tiers. Tier 1 includes self-help tools, digital programmes, and community support — this is where most people start. Use our free BMI calculator to establish your baseline, and our weight converter to track measurements in units you understand. Tier 2 involves GP-led lifestyle programmes and behaviour change support. Tier 3 provides specialist multidisciplinary weight management services, where prescription weight loss medications may be considered alongside diet and exercise. Tier 4 is bariatric surgery for severe obesity with significant health complications. Ask your GP which tier is appropriate for you — eligibility and waiting times vary by region.
- 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 overweight and obese according to NHS guidelines?
According to NHS BMI categories, overweight is a BMI of 25.0–29.9, while obese starts at BMI 30.0. The distinction matters because obese categories carry increased risk of type 2 diabetes, heart disease, and certain cancers. Your GP can explain what your specific BMI means for your health and what support is available.
Can I use the BMI calculator if I'm very tall or very muscular?
BMI is a useful screening tool for most people, but it has limitations. It doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI without high body fat. Additionally, if you're exceptionally tall or have an unusual frame, discuss your personal healthy weight range with your GP rather than relying on BMI alone.
How does the NHS weight loss calculator work?
Our free weight loss calculator helps you understand realistic weight loss timelines based on NHS recommendations. The NHS suggests losing 0.5–1 kg per week through a combination of reduced calorie intake and increased physical activity. If you're considering prescription weight loss medications, our GLP-1 calculator shows projected outcomes based on clinical trial data — though individual results always vary.
Should I see my GP about weight loss?
Yes, if your BMI is in the overweight or obese range, or if you have weight-related health conditions like high blood pressure or prediabetes, speak with your GP. They can assess your individual situation, rule out underlying health issues, and discuss the right support tier for you — whether that's lifestyle changes, digital tools, specialist services, or medication.
How do I know if I'm eligible for NHS weight loss medication?
The NHS considers prescription weight loss treatment for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. However, access is through specialist tier 3 services, not standard GP prescription. Your GP can refer you for assessment. Regional availability and waiting times vary significantly, so discuss current options in your area with your GP.
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.