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
TDEE and Weight Loss — The Science Behind Sustainable Weight Loss
TDEE (Total Daily Energy Expenditure) is the total number of calories your body burns each day at rest and during activity. To lose weight, you need to consume fewer calories than your TDEE — this creates a calorie deficit. The NHS recommends a moderate deficit of around 500 calories per day, which typically results in losing approximately 0.5 to 1 kg per week. Understanding your TDEE is fundamental to weight management in the UK, whether you're making lifestyle changes alone or considering prescription weight loss medication as part of your strategy.
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 TDEE Relates to Calorie Deficit and Weight Loss
TDEE is calculated using your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — plus activity factors. A simple formula is: BMR × activity level (typically 1.2 to 1.9 depending on exercise frequency). Once you know your TDEE, you subtract calories to create a deficit.
For example, if your TDEE is 2,500 calories and you consume 2,000 calories daily, you've created a 500-calorie deficit, resulting in approximately 0.5 kg weight loss per week. The NHS weight loss guidance emphasises that sustainable weight management requires both reduced-calorie diet and increased physical activity. Use our free BMI calculator to assess your current weight category, then estimate your calorie needs based on your height, weight, age, and activity level. A 500–750 calorie daily deficit is generally safe and sustainable without medical supervision; larger deficits should only be attempted under healthcare guidance.
For some adults, prescription weight loss medication like GLP-1 injections may support this process by helping reduce appetite and food intake, making the calorie deficit easier to maintain.
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.
TDEE, Weight Loss Injections, and NHS Weight Management
If you're considering prescription weight loss support — such as Mounjaro or Wegovy — understanding your TDEE remains important. These medications work by reducing hunger and promoting fullness, which helps you naturally consume fewer calories and maintain your deficit. Clinical trials showed that adults using GLP-1 weight loss injections achieved significant results when combining medication with lifestyle changes, including awareness of calorie intake.
For NHS weight loss medication access in the UK, you'll be referred to a tier 3 specialist weight management service from your GP. Private prescription weight loss medication is also available following online clinical assessment. Regardless of your approach — diet and exercise alone, or with medication — tracking your progress with our free progress tracker can help you stay motivated and see real results over time.
- 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 a healthy calorie deficit for weight loss?
The NHS recommends a deficit of around 500 calories per day for safe, sustainable weight loss of 0.5 to 1 kg per week. This typically involves eating 500 fewer calories than your TDEE or burning 500 additional calories through activity — or a combination of both. Larger deficits should only be pursued under medical supervision to avoid muscle loss and nutritional deficiency.
How do I calculate my TDEE?
Calculate your Basal Metabolic Rate (BMR) using your age, weight, height, and sex, then multiply by your activity factor (1.2 for sedentary, 1.55 for moderate activity, 1.9 for very active). Online TDEE calculators are widely available. Your GP or a registered dietitian can also help you estimate your personal TDEE and safe calorie targets.
Can weight loss injections like Wegovy help with TDEE and calorie deficit?
Wegovy (semaglutide) is a GLP-1 injection licensed in the UK for weight management. It works by reducing appetite and promoting feelings of fullness, making it easier to maintain a calorie deficit naturally. Clinical trials showed average weight loss of around 15% body weight. It's prescription-only and used alongside diet and activity changes, not instead of them.
How does BMI relate to TDEE and weight loss?
BMI (Body Mass Index) is a screening tool based on weight and height but doesn't reflect your metabolic rate or TDEE. Two people with the same BMI can have very different TDEEs depending on muscle mass, age, and activity level. Use our free BMI calculator to check your current category, then work with your GP to establish a safe, personalised calorie target based on your health goals.
What's the difference between NHS and private weight loss support in the UK?
NHS weight loss medication access is through tier 3 specialist services (referral from your GP) with variable regional availability and waiting lists. Private prescription weight loss medication is available through online assessment without NHS referral. Both routes require clinical assessment and prescription. Lifestyle changes — diet, activity, and tracking — remain essential alongside any medication.
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.