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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How to Calculate Your BMR — UK Health Guide
BMR (basal metabolic rate) is the number of calories your body burns at rest just to maintain basic functions like breathing, circulation, and cell production. Calculating your BMR helps you understand your daily energy needs and is a useful starting point for weight management planning. The NHS recognises BMR as an important metric alongside BMI when assessing overall health and energy balance. Understanding your BMR can help you set realistic weight loss or weight maintenance targets with your GP.
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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 BMR — Common Formulas
Several formulas can estimate your BMR using your weight, height, age, and sex. The most widely used in UK healthcare settings are the Mifflin-St Jeor equation (most accurate for most adults) and the Harris-Benedict equation (older but still referenced).
Mifflin-St Jeor formula:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
For example, a 35-year-old woman weighing 70kg and 165cm tall would have a BMR of approximately 1,474 kcal per day. This means her body burns roughly 1,474 calories daily at complete rest, before any physical activity is considered. The NHS acknowledges that individual BMR varies based on muscle mass, metabolism, and genetics — your actual figure may differ by 10–20% from calculated estimates.
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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.
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Using BMR for Weight Management — UK Context
Your BMR forms the foundation of your total daily energy expenditure (TDEE). To estimate calories burned during a typical day, multiply your BMR by your activity level factor: sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), or very active (×1.725). For sustainable weight loss aligned with NHS guidance, a calorie deficit of approximately 500 kcal per day typically results in losing around 0.5kg per week. If you're considering prescription weight loss support such as GLP-1 medications like Mounjaro or Wegovy, understanding your BMR and TDEE helps your prescriber assess whether medication is appropriate and set realistic expectations. Use our free BMI calculator alongside BMR calculations to get a complete picture of your health metrics, and track changes over time with our progress tracker.
- 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 calories burned at complete rest. TDEE (total daily energy expenditure) is your BMR multiplied by your activity level, giving total daily calorie burn. For weight management, TDEE is more practical for calculating calorie deficits needed for weight loss.
Why does muscle mass affect BMR?
Muscle tissue is metabolically active and burns calories even at rest, whereas fat tissue burns very few calories. People with more muscle mass have higher BMR. This is why strength training can increase your BMR and support long-term weight management.
Should I use BMR or TDEE for weight loss?
Use TDEE for weight loss planning — it accounts for your actual daily activity. The NHS recommends a deficit of 500 kcal from your TDEE for sustainable 0.5kg weekly loss. Your GP can help you set realistic targets based on your TDEE and health status.
Can BMR change over time?
Yes. BMR decreases slightly with age (approximately 2–8% per decade after age 30) and increases with muscle gain. Severe calorie restriction can temporarily lower BMR. Maintaining muscle through exercise helps preserve BMR as you age.
Is calculating BMR useful if I'm considering weight loss medication?
Yes. Knowing your BMR and TDEE helps your prescriber understand your baseline energy needs and assess whether prescription medication like Mounjaro or Wegovy is appropriate. It also helps set realistic expectations — medication works alongside calorie deficit, not instead of it.
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.