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
Does B12 Help With Weight Loss?
B12 (cobalamin) is an essential vitamin that supports metabolism and energy production, but it's not a weight loss solution on its own. If you have a B12 deficiency, correcting it may help improve energy levels and support normal metabolic function — which can indirectly support weight management efforts. However, B12 supplementation in people with normal B12 levels is unlikely to result in weight loss. For sustainable weight loss in the UK, evidence-based approaches include dietary changes, physical activity, and in some cases, prescription weight loss medication prescribed by your GP or through specialist 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.
What Does B12 Do in the Body?
B12 (cobalamin) is a water-soluble vitamin essential for:
- Red blood cell formation and oxygen transport
- DNA synthesis and cell division
- Nerve function and myelin formation
- Metabolism of fats, proteins, and carbohydrates
- Energy production from food
B12 is naturally found in animal-based foods (meat, fish, eggs, dairy) and is produced by bacteria in the soil and water. A B12 deficiency can cause fatigue, weakness, poor concentration, and reduced metabolic efficiency — all of which may contribute to a more sedentary lifestyle and make weight management harder. However, correcting a deficiency restores normal function rather than enhancing metabolism beyond normal levels. If your GP suspects B12 deficiency (common in vegans, vegetarians, older adults, or those with absorption issues), they can test your B12 level and prescribe supplements if needed.
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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.
B12 and Weight Loss — What the Evidence Shows
Some supplement companies market B12 as a weight loss aid, particularly in the form of injections or high-dose oral supplements. However, there is limited clinical evidence that B12 supplementation causes weight loss in people with adequate B12 levels. A 2020 systematic review in the journal Nutrients found no robust evidence that B12 supplementation alone results in significant weight loss. If you have normal B12 levels and inject additional B12, it will not boost your metabolism or burn extra calories. For sustainable weight loss in the UK, the NHS recommends a combination of reduced-calorie diet, increased physical activity, and behavioural support. If these lifestyle changes alone don't achieve results, your GP can refer you to a tier 3 specialist weight management service, where prescription weight loss medication may be considered.
- 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 B12 injection help you lose weight?
B12 injections help restore normal function if you have a deficiency, but they do not cause weight loss in people with adequate B12 levels. Any perceived weight loss is likely due to improved energy levels enabling more physical activity, not a direct metabolic effect. Always consult your GP before considering any injections.
Can B12 deficiency prevent weight loss?
Yes, B12 deficiency can impair metabolism and cause fatigue, which may make it harder to exercise and manage weight effectively. Correcting a deficiency can restore normal energy and metabolic function, indirectly supporting your weight management efforts.
What is the best way to lose weight in the UK?
The NHS recommends a combination of reduced-calorie diet (around 500 kcal/day deficit for approximately 0.5 kg/week loss), increased physical activity, and behaviour change support. For eligible adults, prescription weight loss medication through specialist services may be offered alongside lifestyle changes.
Should I take B12 supplements for weight loss?
B12 supplements are only beneficial if you have a deficiency. If your B12 level is normal, additional supplementation will not support weight loss. Your GP can test your B12 level and advise whether supplementation is appropriate for you.
How can I check my weight loss progress?
Use our free BMI calculator to track changes in your BMI, our weight converter to monitor weight in different units (kg, stone, lbs), and our progress tracker to log your weight loss journey over time. These tools help you see real progress beyond the scales.
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.