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
Calorie Weight Loss Calculator — How Many Calories to Lose Weight?
Understanding your calorie needs is essential for sustainable weight loss. A calorie deficit — where you consume fewer calories than your body burns — is the foundation of effective weight management in the UK. The NHS recommends losing weight at a safe rate of 0.5 to 1 kg per week, which typically requires a calorie deficit of around 500 kcal per day. This guide explains how to calculate your calorie needs, use a weight loss calculator effectively, and understand the role of prescription weight loss medication alongside dietary changes.
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 Calorie Deficit Works for Weight Loss
A calorie deficit occurs when you consume fewer calories than your body expends through activity, metabolism, and digestion. To lose approximately 0.5 kg (1 lb) per week, you need a deficit of around 500 kcal daily. For 1 kg per week, aim for a 1,000 kcal deficit — though this should only be attempted under medical supervision.
- Basal metabolic rate (BMR) — calories your body burns at rest — varies by age, sex, height, weight, and muscle mass
- Total daily energy expenditure (TDEE) — BMR plus calories burned through activity
- Safe deficit range — 500–750 kcal per day supports sustainable weight loss and preserves muscle mass
- Calorie tracking — apps like MyFitnessPal can help you monitor intake alongside weight management UK programmes
Using our free BMI calculator and weight converter above helps you establish your starting point and track progress in both metric (kg) and imperial (stone) measurements.
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.
Weight Loss Medication and Calorie Intake
For some people, prescription weight loss medication — such as GLP-1 injections like Mounjaro or Wegovy — may support weight loss alongside calorie reduction. These medications may help reduce appetite and food cravings, making it easier to maintain a calorie deficit. However, they work best combined with dietary changes and increased physical activity, not as a replacement for them.
If you're considering prescription weight loss treatment, try our GLP-1 weight loss calculator to estimate potential outcomes at different doses. Always consult your GP about whether weight loss medication is appropriate for your individual circumstances.
- 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.
How many calories do I need to eat to lose weight?
This depends on your personal calorie needs, which vary by age, sex, height, weight, and activity level. A typical starting point is reducing intake by 500 kcal daily for 0.5 kg weekly loss. Use the NHS Weight Loss Plan or speak to your GP for personalised guidance.
Is a very low calorie diet safe?
Very low calorie diets (under 800 kcal daily) should only be followed under medical supervision. The NHS recommends losing 0.5–1 kg per week as sustainable and safe. gradual weight management increases risks including muscle loss and nutritional deficiency.
Can weight loss medication help with calorie deficit?
GLP-1 medications like Wegovy may help by reducing appetite and supporting easier adherence to a reduced-calorie diet. They're prescription-only and require clinical assessment. They work best alongside dietary changes and physical activity, not instead of them.
What's the difference between BMI and calorie needs?
BMI measures weight relative to height and indicates health risk categories. Calorie needs are the actual energy your body requires daily. Both are useful — BMI shows your starting health status; calorie calculations help you create a sustainable weight loss plan.
How do I track my weight loss progress accurately?
Weigh yourself weekly at the same time, ideally on the same day. Use our free progress tracker to log results in kg or stone. Weight naturally fluctuates day-to-day due to hydration and hormones — tracking weekly trends is more accurate than daily measurements.
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.