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
Best Diet For Quick Weight Loss in the UK
Quick weight loss requires a calorie deficit, but the "best" diet depends on what you can sustain. The NHS recommends losing 0.5–1 kg per week alongside lifestyle changes. Whether you choose a low-carb approach, intermittent fasting, or a structured meal plan, success comes from consistency rather than extreme restriction. For adults with a BMI above 27–30, prescription weight management support may be available through your GP or private prescribing, often used alongside dietary changes for better results.
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 Diets That Support Weight Loss
Calorie deficit approach: The most reliable method is eating 500 kcal fewer than you burn daily, which typically leads to ~0.5 kg loss per week. This works with any diet type—the key is consistency.
Low-carbohydrate diets: Effective short-term, often producing 1–2 kg loss in the first two weeks (mostly water). Long-term outcomes are similar to standard calorie restriction.
Intermittent fasting (16:8 or 5:2): Evidence supports modest weight loss when combined with healthy eating. The 16:8 pattern means eating within an 8-hour window; 5:2 involves restricting to 500–600 kcal on two days weekly.
Mediterranean diet: Strong NHS evidence for sustainable weight loss and cardiovascular health. Emphasises whole grains, lean protein, vegetables, and olive oil.
Calculate your personal calorie targets using our free BMI calculator above to determine a healthy weight range for your height.
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.
When Weight Loss Injections May Help
If you've tried diet and exercise alone without lasting results, prescription weight loss medication may be offered by your GP through NHS weight management services or via private prescribing. GLP-1 weight loss injections like Wegovy work alongside dietary changes—they're not replacements for a healthy diet, but they can reduce appetite and cravings, making a calorie deficit easier to maintain.
Our GLP-1 weight loss calculator can help you estimate potential outcomes at different medication doses. However, any prescription medication requires a clinical assessment to check suitability. Always speak to your GP or a prescriber before starting weight loss medication.
Use our free progress tracker to log your weight loss journey week by week, regardless of your approach. Tracking progress visually increases motivation and helps identify what works for your lifestyle.
- 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 is the fastest safe rate of weight loss?
The NHS recommends losing 0.5–1 kg (1–2 lbs) per week. Faster loss often results in muscle loss and is harder to sustain. Very gradual weight management (over 1.5 kg weekly) should only happen under medical supervision, such as with a supervised very low-calorie diet.
Is low-carb or low-fat diet better for quick weight loss?
Both work through calorie deficit. Low-carb can produce faster initial loss (due to water weight), but long-term results are similar. Choose whichever you can stick to—sustainability matters more than the diet type.
Can I lose weight quickly without changing my diet?
Unlikely. Weight loss fundamentally requires a calorie deficit. Exercise supports health and preserves muscle but must be combined with eating fewer calories. For significant rapid loss, diet change is essential.
Is prescription weight loss medication available on the NHS?
Yes, through NHS tier 3 specialist weight management services if you meet eligibility criteria (BMI 30+, or 27+ with health conditions). However, waiting lists are long in many regions. Private prescribing is available without an NHS referral, though costs apply.
Do weight loss diets work long-term?
Only if you can maintain them. The best diet is one you'll follow consistently. Most successful weight loss combines structured eating with lifestyle habit changes, physical activity, and often support from a GP or weight management programme.
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.