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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Weight Reduction Calculator — Plan Your Health Goals
A weight reduction calculator is a practical tool to help you estimate realistic weight loss targets and track your progress towards a healthier weight. Whether you're managing your weight through lifestyle changes, working with your GP, or considering prescription options like Wegovy or Mounjaro, understanding your current health metrics and projected outcomes is essential. This guide explains how weight reduction calculators work, how they fit into UK health management, and how to use them effectively alongside NHS guidance and evidence-based approaches.
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.
How Weight Reduction Calculators Work
A weight reduction calculator combines your current weight, target weight, and personal information to estimate how long sustainable weight loss might take and what results you could reasonably expect. Most calculators use your age, sex, current weight, height, and activity level to project outcomes based on calorie deficit principles.
The NHS recommends losing 0.5 to 1 kg per week for sustainable, safe weight loss — this equals approximately 500 calories per day deficit. A weight reduction calculator applies this science to your specific numbers. If you're considering prescription weight loss medication, our free GLP-1 weight loss calculator can help estimate potential weight loss at different doses of Wegovy (semaglutide) or Mounjaro (tirzepatide), alongside your lifestyle changes.
Key inputs for any reduction calculator include:
- Current weight (use our weight converter to switch between kg, stone, and lbs)
- Target weight or target BMI
- Activity level and exercise commitment
- Dietary approach and calorie goals
- Any medications or health conditions affecting weight
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.
Using Calculators With NHS Guidance and Healthy Weight Management
Weight reduction calculators are most effective when used alongside broader healthy weight management strategies. Start by calculating your current BMI using the free BMI calculator on this page — this shows you where you stand against NHS healthy weight guidelines (BMI 18.5–24.9 for most adults, or 18.5–22.9 for South Asian, Chinese, Black African, and Black Caribbean adults).
Then use a weight reduction calculator to set realistic targets: aim to reach the upper healthy weight range first, which is often more sustainable than aiming for the lower bound immediately. Track your actual progress using our free progress tracker, which records real weight changes weekly or monthly so you can compare estimated vs actual results.
Remember: calculators provide estimates only. Individual results vary based on genetics, metabolism, adherence, and health factors. Always discuss your weight loss plan with your GP, especially if you're considering prescription medications or 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 is a weight reduction calculator?
A weight reduction calculator is a tool that estimates how long it might take to reach your target weight based on your current weight, activity level, and calorie deficit. It uses NHS-recommended loss rates (0.5–1 kg per week) to project realistic timelines and track progress toward healthy weight management goals.
How accurate are weight reduction calculators?
Calculators provide helpful estimates but are not assured. Actual weight loss depends on many factors including metabolism, genetics, adherence to diet and exercise, medical conditions, medications, and hormonal changes. Use calculators as a guide, not a prediction, and compare estimates against real progress using a progress tracker.
What's the difference between a weight reduction calculator and a BMI calculator?
A BMI calculator shows your current health category (underweight, healthy, overweight, obese) based on your height and weight. A weight reduction calculator projects future weight loss timelines. Use both: check your BMI first to understand your starting point, then use a reduction calculator to set realistic targets and timelines.
Can I use a weight reduction calculator if I'm taking Wegovy or Mounjaro?
Yes. Our free GLP-1 weight loss calculator is specifically designed for this, showing estimated weight loss at different doses alongside your lifestyle changes. Prescription medications like Wegovy (semaglutide) and Mounjaro (tirzepatide) are used alongside diet and exercise, not instead of them, so calculators help you plan realistic outcomes.
What should my target weight be according to NHS guidance?
Your healthy weight range is between BMI 18.5 and 24.9 (or 18.5–22.9 if you're of South Asian, Chinese, Black African, or Black Caribbean heritage). Use the BMI calculator to find your healthy range in kg and stone, then use a weight reduction calculator to plan realistic steps toward that range.
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.