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
Vitamin D and Weight Loss — What UK Science Shows
Vitamin D is essential for bone health, immunity, and mood regulation. Emerging research suggests a link between vitamin D deficiency and weight gain, but vitamin D alone is not a weight loss solution. If you're considering weight management in the UK, this guide covers what the evidence shows about vitamin D, plus the prescription weight loss options available to eligible adults through NHS and private services.
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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.
Prescription Weight Loss Options in the UK
For adults struggling with excess weight, the UK now offers several prescription weight management medications alongside lifestyle changes. These are licensed for people with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure.
- Mounjaro (tirzepatide) — a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist, helping to reduce appetite and regulate blood sugar. Clinical trials showed an average weight loss of 15–21% body weight over 72 weeks.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection available for weight management. Average weight loss in trials was approximately 15% body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection, also licensed for weight management in the UK.
All are prescription-only and require a clinical assessment before being prescribed. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check your personal BMI status.
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 — How to Get Started
NHS access: Ask your GP to refer you to your local specialist weight management service (tier 3). Availability varies by region, and waiting times can be lengthy. NHS services are free but access depends on your local commissioning arrangements.
Private access: Available through online consultations with UK-licensed prescribers, followed by dispensing via GPhC-registered pharmacies. Private options don't require an NHS referral and are usually faster, though costs vary by dose and provider.
Either way, weight loss medication works best alongside a reduced-calorie diet and increased physical activity. Track your progress with our free progress tracker once you start your weight management journey.
- 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.
Does vitamin D deficiency cause weight gain?
Some research suggests a link between low vitamin D and higher body weight, possibly through effects on appetite regulation and metabolism. However, vitamin D deficiency is not a direct cause of weight gain. Low vitamin D is common in the UK — around 1 in 5 adults are deficient. If concerned, ask your GP about vitamin D testing.
Is vitamin D supplementation alone enough for weight loss?
No. Vitamin D is vital for health, but supplementation alone will not produce weight loss. Sustainable weight loss requires a calorie deficit combined with physical activity. If you're eligible for prescription weight management medication, your GP or a licensed prescriber can assess whether treatment is appropriate for you.
What does the NHS say about vitamin D and weight?
The NHS recommends all adults take a 10 micrograms (400 IU) vitamin D supplement during autumn and winter. While adequate vitamin D supports overall health, the NHS emphasizes that weight management requires calorie reduction, physical activity, and — for eligible individuals — prescription medication if recommended.
How can I check if I'm eligible for prescription weight loss treatment in the UK?
You're potentially eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Speak with your GP or use our free BMI calculator to check your status. A licensed prescriber will conduct a full clinical assessment before prescribing any medication.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with average weight loss around 15–21% body weight. Wegovy (semaglutide) is a GLP-1 agonist alone with average weight loss around 15% body weight. Individual results vary significantly. Your prescriber will discuss which option 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.