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
Understanding Your Basal Metabolism
Basal metabolism is the amount of energy your body uses at rest just to keep you alive — breathing, circulating blood, maintaining body temperature, and cell function. It accounts for roughly 60–70% of your total daily energy expenditure. Your basal metabolic rate (BMR) is unique to you and depends on age, sex, body composition, height, weight, and genetics. Understanding your BMR is helpful when managing your weight, as it forms the foundation for calculating how many calories you need to maintain, lose, or gain weight. Use our free BMI calculator alongside this guide to assess your current healthy weight range for your height.
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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 Basal Metabolism Works and What Affects It
Your basal metabolism is driven by essential body processes: your heart beating, lungs breathing, kidneys filtering, and your brain functioning all require constant energy. Muscle tissue is metabolically active — meaning it burns calories even when you're at rest — whereas fat tissue burns very few calories when inactive. This is why people with more muscle mass typically have a higher BMR than those with more body fat, even at the same weight.
Factors that affect your BMR include:
- Age: BMR naturally decreases by about 2–8% per decade after age 30
- Sex: Men typically have a higher BMR than women due to greater muscle mass
- Body composition: More muscle = higher BMR; more fat = lower BMR
- Height and weight: Larger bodies require more energy to function
- Genetics: Some people naturally have faster or slower metabolism
- Hormones: Thyroid function, cortisol, and oestrogen affect metabolic rate
- Medical conditions: PCOS, thyroid disorders, and diabetes can alter metabolism
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.
Basal Metabolism and Weight Management
Knowing your approximate BMR helps you understand how many calories your body needs daily. A typical calculation adds activity levels on top of your BMR to find your total daily energy expenditure (TDEE). For sustainable weight loss, NHS guidance recommends creating a calorie deficit of around 500 kcal per day, which typically results in losing approximately 0.5–1 kg per week. Conversely, if you're underweight, you need to eat above your BMR plus activity calories to gain weight. Our free weight converter and BMI calculator can help you assess whether your current weight is within a healthy range for your height, and then use that context to set realistic weight management goals with your GP if needed.
- 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 the difference between basal metabolism and total daily energy expenditure?
Basal metabolism (BMR) is the energy your body uses at complete rest — roughly 60–70% of your daily calorie burn. Total daily energy expenditure (TDEE) includes your BMR plus calories burned through activity, exercise, and digestion. To lose weight sustainably, you need to eat fewer calories than your TDEE, not necessarily below your BMR.
Can you increase your basal metabolism?
Yes, several factors can modestly increase BMR: building muscle through resistance exercise (muscle is metabolically active), eating adequate protein, staying hydrated, and getting enough sleep. Extreme calorie restriction actually *lowers* BMR — this is why sustainable, moderate calorie deficits work better for long-term weight loss than crash dieting.
Does basal metabolism slow down with age?
Yes. Basal metabolism naturally decreases by about 2–8% per decade after age 30, primarily because people tend to lose muscle mass as they age. Staying physically active and maintaining muscle through strength training can help slow this decline and support healthy weight management throughout life.
How can I calculate my basal metabolic rate?
Several formulas exist, such as the Harris-Benedict or Mifflin-St Jeor equation, which use your age, sex, height, and weight. Many online calculators can estimate your BMR — use your result as a starting point. For personalised guidance on your specific metabolic needs, speak with your GP or a registered dietitian.
Does basal metabolism affect weight loss with medications like semaglutide?
Indirectly, yes. GLP-1 medications like Wegovy work by reducing appetite and food intake, which creates a calorie deficit. Your baseline BMR determines how many calories you burn at rest — a higher BMR means a bigger total calorie deficit at the same food intake. Combined with physical activity and reduced-calorie diet, this supports weight loss alongside medication use.
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.