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 You Need to Know
Vitamin D plays an important role in weight management, metabolism, and overall health. Many UK adults have insufficient vitamin D levels, particularly during winter months. While supplementing vitamin D alone is not a weight loss solution, maintaining adequate levels supports healthy weight management. For adults struggling with excess weight, prescription weight management medication is available in the UK alongside lifestyle changes and proper nutrition.
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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
UK-licensed prescription weight management medications are available for adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea.
Three main options are licensed in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injected once weekly. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks when combined with dietary changes.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly, with average weight loss of approximately 15% of body weight in clinical trials.
- Saxenda (liraglutide) — a daily GLP-1 injection option, typically resulting in 5–clinically studied weight loss.
All three are prescription-only and require a clinical assessment to confirm eligibility and suitability. Use our free GLP-1 weight loss calculator to understand how these medications might support weight loss when combined with a reduced-calorie diet and increased physical activity.
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 and Getting Started
NHS access to prescription weight loss medication is through specialist tier 3 weight management services. Your GP can refer you if you meet criteria, though waiting lists vary significantly by region. Private access is available through UK-licensed prescribers following an online clinical assessment — no NHS referral needed.
Either route requires confirmation that weight loss medication is appropriate for your individual health situation. Your GP can advise on NHS options in your area, eligibility based on your BMI and health conditions, and whether prescription medication aligns with your weight management goals. Calculate your personal BMI using our free BMI calculator to understand where you stand and what conversations to have with your healthcare provider.
- 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?
Research suggests vitamin D deficiency may be associated with weight gain and metabolic dysfunction, but deficiency alone does not directly cause weight gain. Adequate vitamin D supports healthy metabolism and insulin function. Weight gain is multifactorial—involving diet, activity, genetics, and medical conditions. If you suspect vitamin D deficiency, ask your GP about testing and supplementation as part of overall health management.
Can I lose weight just by taking vitamin D supplements?
No. Vitamin D supplementation alone is not a weight loss treatment. It supports overall health and may help optimise metabolic function when levels are low, but sustainable weight loss requires a reduced-calorie diet and increased physical activity. For significant weight loss support, prescription medications like Mounjaro or Wegovy are available for eligible UK adults.
What is the link between vitamin D and GLP-1 medications like Mounjaro?
Both vitamin D and GLP-1 medications support metabolic health, but through different mechanisms. Adequate vitamin D optimises insulin sensitivity and metabolic function. GLP-1 medications directly reduce appetite and support weight loss. Together—alongside a healthy diet—they may provide complementary benefits. Always discuss supplements with your prescriber when taking weight loss medication.
How do I know if I'm eligible for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as diabetes, high blood pressure, or sleep apnoea. An assessment by a GP or licensed prescriber will confirm suitability. Use our free BMI calculator to check your current BMI and discuss options with your GP.
Should I take vitamin D while using Mounjaro or Wegovy?
This depends on your individual vitamin D levels and medical history. Some people benefit from vitamin D supplementation alongside GLP-1 medication. Always inform your prescriber of all supplements you take—they can advise whether vitamin D supplementation is appropriate and at what dose for your situation.
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.