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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BMR Weight Loss Calculator — Understand Your Metabolic Rate
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at rest just to keep functioning. Understanding your BMR is essential for effective weight loss UK, as it forms the foundation of any calorie deficit strategy. Whether you're considering lifestyle changes or exploring weight management options, knowing your BMR helps you set realistic goals and track your progress. Combined with your activity level, BMR determines your total daily energy expenditure — the key to sustainable weight loss.
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 to Calculate Your BMR — The Two Main Formulas
The two most widely used BMR formulas are the Mifflin-St Jeor equation (most accurate for modern populations) and the Harris-Benedict formula (older but still commonly referenced). Both require your weight in kg, height in cm, age, and sex.
Mifflin-St Jeor Formula (recommended):
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
For example, a 30-year-old woman weighing 70kg and 165cm tall would have a BMR of approximately 1,385 kcal per day. Use our free BMI calculator and weight converter above to check your measurements in metric units, then apply these formulas to find your personal BMR.
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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.
Using BMR for Weight Loss — Creating Your Calorie Deficit
Once you know your BMR, multiply it by your activity factor to calculate your Total Daily Energy Expenditure (TDEE). For weight loss UK, the NHS recommends a deficit of approximately 500 kcal per day for sustainable loss of around 0.5kg per week. This means eating 500 kcal fewer than your TDEE.
Activity factors: Sedentary (BMR × 1.2), lightly active (BMR × 1.375), moderately active (BMR × 1.55), very active (BMR × 1.725). Prescription weight loss medication combined with reduced-calorie eating can help achieve and maintain this deficit. Our GLP-1 weight loss calculator can help you project potential results when combining lifestyle changes with clinical options.
- 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 BMR and TDEE?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just to maintain basic functions like breathing and heart rate. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by your activity level, representing total calories burned in a day including exercise. For weight loss, you create a deficit from your TDEE, not your BMR.
Can BMR change over time?
Yes. BMR naturally decreases with age (approximately 2% per decade after age 30) due to muscle loss. However, building muscle through strength training can increase BMR. gradual weight management can also lower BMR temporarily. This is why sustainable, gradual weight loss UK is more effective than crash dieting.
Is BMR the same for everyone at the same weight and height?
No. Individual BMR varies due to genetics, muscle mass, hormones, medical conditions, and metabolic health. Two people of the same weight and height can have different BMRs. This is why personalised assessment from a GP or healthcare professional is valuable when considering weight management options.
How does prescription weight loss medication fit with BMR calculations?
Prescription weight loss medications like GLP-1 injections work alongside calorie deficit by reducing appetite and supporting feelings of fullness, making it easier to maintain your calculated deficit. They don't change your BMR directly, but help you stick to reduced-calorie eating. Our GLP-1 calculator can help estimate potential results with medication support.
Should I eat below my BMR to lose weight faster?
No. Eating below your BMR for extended periods is dangerous and can slow metabolism, cause muscle loss, nutritional deficiencies, and fatigue. The NHS recommends never consuming fewer than 1,200 kcal per day for women or 1,500 kcal for men without medical supervision. Consult your GP for personalised guidance on safe weight loss UK.
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.