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
Weight Loss Calculator: Estimate Your Progress
A weight loss calculator helps you plan realistic weight loss goals and track potential progress based on your current weight, height, and chosen weight management method. Whether you're considering prescription weight loss medication like Wegovy or Mounjaro, following NHS weight loss guidance, or simply calculating calorie deficit, a calculator gives you personalised projections based on your individual circumstances. MyWeightCheck offers free weight loss and BMI calculators to help UK adults understand their weight health and plan effective strategies.
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 Loss Calculators Work
A weight loss calculator uses your personal data — weight, height, age, sex, and activity level — to estimate how quickly you might lose weight under different scenarios. Most calculators work by calculating your Basal Metabolic Rate (BMR), which is the number of calories your body burns at rest, then adjusting for activity level to estimate your daily calorie needs. If you create a calorie deficit (eating fewer calories than you burn), the calculator projects weight loss: a deficit of approximately 500 kcal per day typically results in losing around 0.5 kg per week, which aligns with NHS weight loss guidance. For those interested in GLP-1 weight loss medication, specialised calculators use clinical trial data from drugs like Wegovy (semaglutide) and Mounjaro (tirzepatide) to project potential weight loss at different doses — though individual results vary significantly. Our free GLP-1 weight loss calculator helps estimate realistic outcomes based on the latest clinical evidence from STEP and SURMOUNT trials.
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.
Types of Weight Loss Calculators Available
Different calculators serve different purposes in weight management UK planning. Calorie deficit calculators estimate weight loss based purely on diet and exercise changes. GLP-1 weight loss calculators project outcomes with prescription medications like Wegovy or Mounjaro based on clinical trial averages. BMI-based calculators show your current weight category and healthy weight range for your height — use our free BMI calculator above to check yours instantly. Macro calculators break down protein, carbohydrate, and fat targets. Progress trackers log your actual weight loss over time and compare it against your projections. Most weight management UK success comes from combining a calculator's projections with realistic lifestyle changes and, where appropriate, professional medical support from your GP or a specialist service.
- 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 weight loss can I expect with a weight loss calculator?
Weight loss calculators provide estimates based on average outcomes from clinical trials or calorie mathematics. With a 500 kcal daily deficit, you may lose approximately 0.5 kg per week. With GLP-1 medication like Wegovy, clinical trials showed average weight loss of around 15% of body weight at the highest dose, though individual results vary significantly. Always remember that calculators are estimates — your actual results depend on adherence, metabolism, and other factors. Consult your GP for personalised advice.
Is a weight loss calculator accurate for everyone?
Weight loss calculators provide useful estimates but have limitations. They don't account for individual metabolic differences, hormonal factors, medical conditions, medications, or genetics — all of which affect real-world weight loss. Calculators work best as planning tools rather than exact predictors. For prescription weight loss medication guidance, a clinical assessment with a prescriber is essential, as they'll assess your individual eligibility and suitability based on your full health picture, not just calculator results.
Can I use a weight loss calculator if I'm taking Mounjaro or Wegovy?
Yes — our free GLP-1 weight loss calculator is designed specifically for those considering or using prescription weight management medications. It uses data from clinical trials (STEP trial for Wegovy, SURMOUNT trial for Mounjaro) to project potential weight loss at different doses. However, the calculator provides estimates only. Your actual results depend on your dose, adherence, diet, activity level, and individual response. Always discuss your progress and expectations with your prescriber.
What's the difference between a weight loss calculator and a BMI calculator?
A BMI calculator determines your current weight category (underweight, healthy weight, overweight, or obese) based on your height and weight. A weight loss calculator estimates how much weight you might lose over time under specific conditions. Both are useful: use our free BMI calculator to understand where you stand now, and our weight loss calculator to project future progress. Together, they help you set realistic goals aligned with NHS weight management UK guidance.
Should I use a weight loss calculator before seeing my GP?
Yes — using a calculator beforehand can help you understand your baseline BMI, healthy weight range, and realistic progress expectations, which makes your GP conversation more productive. However, a calculator is not a substitute for professional medical advice. Your GP can assess your individual health, recommend appropriate tier interventions (from self-help through to specialist services), and discuss whether prescription weight loss medication is suitable for you based on your full health picture, not just calculator estimates.
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.