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
Why Diet and Exercise Aren't Always Enough for Weight Loss
You're eating less, moving more, but the scales aren't budging. This is incredibly common and doesn't mean you're doing anything wrong. Many people find that diet and exercise alone cannot overcome metabolic, hormonal, or medical factors affecting weight management in the UK. Understanding why this happens — and what options exist — can help you take a more effective approach to your health. Using our free BMI calculator above can help track where you stand healthwise, while exploring all available weight management strategies may reveal solutions that work better for your situation.
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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.
Why Diet and Exercise Alone May Not Be Enough
Weight loss is not simply about calories in versus calories out. Several factors can prevent weight loss even when you're following a strict diet and exercise routine:
- Metabolic adaptation: Your body adapts to sustained calorie deficit by lowering metabolic rate, making further loss harder
- Hormonal imbalances: Insulin resistance, thyroid problems, or polycystic ovary syndrome (PCOS) can make weight loss extremely difficult
- Medications: Some prescription drugs (antidepressants, corticosteroids, diabetes medications) increase appetite or slow metabolism
- Medical conditions: Type 2 diabetes, sleep apnoea, and depression all make weight loss more challenging
- Genetics: Your genetic background significantly influences how your body stores and loses weight
- Age and hormonal changes: Menopause, andropause, and natural metabolic decline with age reduce weight loss effectiveness
This is why NHS weight loss guidance recognises that lifestyle changes alone don't work for everyone, and why prescription weight loss medication exists as part of a comprehensive approach.
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.
Prescription Weight Loss Support in the UK
If diet and exercise haven't delivered results after 3–6 months of genuine effort, prescription weight loss medication may be an option. GLP-1 weight loss medications like Wegovy (semaglutide) and Mounjaro (tirzepatide) are licensed in the UK for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes or high blood pressure.
These medications work differently than willpower alone — they reduce appetite, help you feel fuller faster, and support better food choices. Our free GLP-1 weight loss calculator can help you estimate potential results, and they're always used alongside continued dietary changes and physical activity, not instead of them. Access through NHS specialist services varies by region, but private prescription options are also available following clinical assessment.
- 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 long should I try diet and exercise before considering medication?
Most weight management guidelines recommend a genuine 3–6 month attempt at dietary changes and increased physical activity before considering medication. However, if you have significant obesity or weight-related health conditions, discussing medication options with your GP earlier is reasonable. Individual circumstances vary.
Could my medications be preventing weight loss?
Yes. Antidepressants, some diabetes medications, corticosteroids, and antipsychotics can increase appetite or slow metabolism. If you suspect your medication is affecting weight, discuss this with your GP — never stop taking prescribed medication without guidance, but alternative options may exist.
Is my thyroid stopping me from losing weight?
Thyroid problems, particularly hypothyroidism, can significantly reduce weight loss. If you haven't had thyroid function tests (TSH and free T4), ask your GP for these. If you have hypothyroidism, proper thyroid hormone replacement should support weight loss better, though it may take weeks to optimise.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is licensed in the UK specifically for weight management at 2.4 mg once weekly. Ozempic is licensed for type 2 diabetes (up to 2 mg) — using it for weight loss is off-label. Wegovy is the appropriate licensed choice for weight management.
Can I use a weight loss injection if I'm already exercising and dieting?
Yes. GLP-1 medications like Wegovy are designed to work alongside continued diet and exercise, not replace them. The medication supports your efforts by reducing appetite and cravings, making it easier to maintain dietary changes and stay consistent with physical activity.
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.