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 Work Out Your Basal Metabolic Rate
Your basal metabolic rate (BMR) is the number of calories your body burns at rest just to maintain basic functions like breathing, circulation, and cell production. Understanding your BMR is essential for healthy weight management because it forms the foundation of your daily calorie needs. Whether you're looking to lose weight, maintain your current weight, or understand your metabolism better, calculating your BMR is a practical first step. This UK health guide explains what BMR is, how to calculate it, and how it relates to your overall energy expenditure and weight management goals.
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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.
BMR Formulas and How to Calculate Yours
There are two main formulas for calculating basal metabolic rate: the Harris-Benedict equation (revised 1984) and the Mifflin-St Jeor equation (more accurate for modern populations). The Mifflin-St Jeor formula is generally preferred by NHS-aligned health professionals and is considered more accurate for average adults.
Mifflin-St Jeor Formula for BMR:
- 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 35-year-old woman weighing 70kg and 165cm tall would calculate: (10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 1,437 calories per day at rest. Once you have your BMR, you can calculate your total daily energy expenditure (TDEE) by multiplying BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active).
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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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BMR, Weight Management, and Healthy Weight Context
Your BMR provides important context for weight management decisions. The NHS recommends a sustainable calorie deficit of around 500 kcal per day for safe, gradual weight loss of approximately 0.5–1 kg per week. Knowing your BMR helps you understand how much you can reduce calories without going too low. For instance, if your BMR is 1,437 kcal and your TDEE is around 1,700 kcal (sedentary lifestyle), a deficit of 500 kcal would mean consuming approximately 1,200 kcal daily — which requires careful planning to ensure adequate nutrition.
Use our free BMI calculator alongside your BMR calculation to understand your full metabolic and weight health picture. Our weight converter makes it easy to switch between kg, stone, and lbs when inputting your weight into formulas. If you're considering weight management options, including prescription weight loss support, our GLP-1 weight loss calculator can help you project potential outcomes based on different treatment approaches.
- 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 number of calories your body burns at complete rest. TDEE (total daily energy expenditure) is your BMR multiplied by your activity level, reflecting total daily calorie burn including exercise and daily movement. For weight management, you need your TDEE to understand how much you can safely reduce calories.
How accurate are BMR formulas?
BMR formulas are estimates based on population averages. The Mifflin-St Jeor equation is accurate within about ±10% for most people. Individual variation exists based on muscle mass, metabolism, medical conditions, and genetics. Your GP can discuss more precise metabolic testing if needed.
Does BMR change with weight loss?
Yes. As you lose weight, your BMR decreases slightly because there's less body mass to maintain. This is why weight loss can plateau over time. Maintaining muscle through strength training during weight loss helps preserve BMR.
Can I use BMR to plan a weight loss diet?
BMR helps you understand your baseline, but it's only part of the picture. The NHS recommends a 500 kcal deficit for safe 0.5–1 kg weekly loss. If you're considering prescription weight loss medication alongside dietary changes, discuss your calorie targets with your GP or prescriber.
Is BMR related to being overweight or obese?
BMR itself isn't directly related to BMI category, but understanding both together is useful. Use our free BMI calculator to check your weight category, then calculate BMR to understand your calorie needs for sustainable weight management within a healthy 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.