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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Calorie Counter for Weight Loss in the UK
Tracking calories is a fundamental part of weight loss, but it's just one piece of the puzzle. In the UK, many people combine calorie tracking with lifestyle changes—and for those who meet eligibility criteria, prescription weight management options like Mounjaro and Wegovy are also available. Whether you're counting calories manually or using an app, understanding how calorie deficit works alongside other weight loss approaches can help you make informed decisions about your health. Our free BMI calculator and GLP-1 weight loss calculator can help you understand your current health status and explore what might work for you.
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.
UK Prescription Weight Loss Options Alongside Calorie Tracking
For many adults in the UK, calorie counting alone works well—a deficit of around 500 kcal per day typically results in losing approximately 0.5 kg per week. However, prescription weight management medications can provide additional support if you're eligible. Mounjaro (tirzepatide) and Wegovy (semaglutide) are UK-licensed GLP-1 medications that may help reduce appetite and support feeling fuller after meals, making it easier to maintain a calorie deficit naturally. Saxenda (liraglutide) is also available as a once-daily option. These prescription medications work best alongside a reduced-calorie diet and increased physical activity—they're not replacements for lifestyle changes, but tools to help make those changes more manageable. In clinical trials, eligible adults using these medications alongside calorie reduction and exercise achieved an average weight loss of 15–21% of body weight, though individual results vary significantly.
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.
NHS vs. Private Access to Weight Management Support in the UK
If you're interested in prescription weight loss medication, you have two main routes in the UK. NHS access is through specialist tier 3 weight management services—your GP can refer you, though waiting lists vary significantly by region. Private access is available through online prescribing services; you complete a clinical assessment with a UK-licensed prescriber, and if you're eligible, a prescription is issued by a GPhC-registered pharmacy. Either route requires a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. Regardless of route, prescription weight loss medications are always paired with calorie reduction and lifestyle support for best results. Our free weight loss calculator can help you estimate potential outcomes at different medication doses.
- 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 should I be in deficit to lose weight?
The NHS recommends a deficit of around 500 kcal per day for sustainable weight loss of approximately 0.5 kg (1 lb) per week. A very low-calorie diet under 800 kcal should only be followed under medical supervision. Most people find a moderate deficit combined with increased activity most sustainable long-term.
Can I use a calorie counter app alongside prescription weight loss medication?
Yes, absolutely. Apps like MyFitnessPal or Cronometer work well alongside Mounjaro, Wegovy, or Saxenda. Many people find that prescription medication actually makes calorie tracking easier because appetite reduction naturally leads to lower intake. Always discuss any new apps or dietary changes with your prescriber.
How do I know if I'm eligible for prescription weight loss medication in the UK?
You're likely eligible if your BMI is 30 or above, or 27 or above with a weight-related health condition (diabetes, high blood pressure, sleep apnoea, cardiovascular disease). Use our free BMI calculator to check your current BMI, then speak with your GP about NHS referral options or explore private prescribing services.
Which is better—Mounjaro or Wegovy for weight loss?
Clinical trials show both are effective. Mounjaro (dual GIP+GLP-1) showed average weight loss of 15–21%, while Wegovy (GLP-1 only) showed around 15%. Individual results vary considerably. Your prescriber will recommend the most suitable option based on your health history and preferences.
Do I still need to count calories if I'm taking a GLP-1 medication?
Prescription weight loss medications like Mounjaro and Wegovy work best alongside a reduced-calorie diet—they're not a replacement for dietary changes. Many people find they naturally eat less because appetite is reduced, but some still track calories to ensure they're in a meaningful deficit. Your healthcare team can advise what approach suits you best.
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.