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
What Is the Best Weight Loss Diet?
There's no single "best" weight loss diet — what works depends on your lifestyle, preferences, and health. However, evidence-based approaches like calorie deficit diets, the Mediterranean diet, and structured NHS weight management programmes have strong scientific support. The key to sustainable weight loss isn't finding a perfect diet, but choosing an approach you can stick to long-term alongside increased physical activity. Our BMI calculator can help you understand where you currently stand, and you can use our free weight converter to track your progress in the units that matter to 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.
Evidence-Based Weight Loss Approaches in the UK
The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results. This typically requires a calorie deficit of around 500 kcal per day. Several evidence-based diets have proven effective for weight management in UK health contexts:
- Calorie deficit diet: Simply eating fewer calories than you burn. No foods are off-limits, making it flexible and sustainable.
- Mediterranean diet: Emphasis on vegetables, olive oil, fish, and whole grains. Strong evidence for cardiovascular health and long-term adherence.
- Intermittent fasting (IF): Approaches like 16:8 (fasting 16 hours, eating within 8 hours) or 5:2 (eating normally 5 days, restricted calories 2 days). Evidence supports modest weight loss, though results vary.
- Low-carbohydrate diet: Effective for short-term weight loss, though long-term outcomes are similar to standard calorie restriction.
- NHS Weight Loss Plan: Free 12-week programme combining dietary and behavioural support, available through some GP practices and online.
Research shows that consistency matters more than which specific diet you choose. The "best" diet is one you can maintain long-term.
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.
Role of Weight Loss Medication in Your Weight Management Journey
For some people, prescription weight loss medication may support their efforts alongside diet and exercise. Prescription weight loss injections like GLP-1 medications are available in the UK for people with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes or high blood pressure. Our GLP-1 weight loss calculator can help you estimate potential weight loss outcomes at different doses if you're exploring medication options. These medicines work by reducing appetite and helping you feel fuller after smaller meals. However, medication is never a substitute for dietary changes and physical activity — it's used alongside them. Your GP or a prescriber can assess whether prescription weight loss treatment is appropriate for you after a 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.
What's the fastest weight loss diet?
gradual weight management diets (over 1.5 kg per week) can work short-term but often aren't sustainable and may cause muscle loss. The NHS recommends 0.5–1 kg per week for safety and sustainability. Very low-calorie diets (under 800 kcal/day) should only be followed under medical supervision. Speed isn't the goal — lasting results are.
Is low-carb or low-fat better for weight loss?
Both can work. Research shows that long-term weight loss is similar between low-carb and low-fat diets when calories are controlled. The best diet is whichever one you can stick to consistently. Some people find low-carb easier because protein and fat increase satiety; others prefer balanced approaches.
How do I know if a weight loss diet is working?
Track progress using multiple measures: weekly weigh-ins (same day/time), how your clothes fit, waist circumference, and energy levels. Our free progress tracker helps log your journey. Don't fixate on daily fluctuations — weight naturally varies by 1–2 kg due to water retention and digestion.
Can diet alone achieve weight loss, or do I need exercise?
Diet is the primary driver of weight loss — you can lose weight through calorie deficit alone. However, exercise supports cardiovascular health, preserves muscle mass during weight loss, and improves long-term weight maintenance. Combining both diet and activity is ideal.
Should I use my BMI to guide weight loss targets?
Yes. Use our BMI calculator to establish a healthy weight range for your height. According to NHS guidelines, a BMI of 18.5–24.9 is healthy for most adults (lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean backgrounds). Your GP can discuss personalised targets.
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.