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 Happens to Your Skin After Weight Loss
When you lose a significant amount of weight through diet, exercise, or prescription weight loss medication, your skin may not shrink at the same rate as the fat beneath it. This can result in loose or sagging skin — a common concern for people achieving substantial weight loss in the UK. Understanding what causes this, how long it takes, and what you can do about it helps you make informed decisions about your weight management journey.
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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 Loose Skin Occurs During Weight Loss
Your skin contains collagen and elastin — proteins that provide elasticity and allow skin to stretch and contract. When you carry excess weight for a long time, your skin stretches to accommodate it. As you lose weight, especially if loss is rapid or substantial, your skin may not fully retract because:
- Collagen and elastin naturally decline with age and sun exposure
- gradual weight management gives skin less time to adjust gradually
- The amount of loose skin depends on how long you carried the excess weight, your age, genetics, and how much weight you've lost
- Younger skin typically has better elasticity and may recover more completely than older skin
Loose skin is particularly common after losing 20% or more of your body weight. Using our BMI calculator can help you set realistic weight loss goals and understand your current health range.
Clinically BackedWeight Loss
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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.
Managing Loose Skin — Practical Strategies
Several evidence-based approaches can help minimise loose skin or improve its appearance:
- Gradual weight loss: Losing weight at the NHS-recommended rate of 0.5–1 kg per week gives your skin time to adjust naturally
- Strength training: Building muscle underneath loose skin can help fill it out and improve appearance
- Hydration and nutrition: Adequate water intake and protein support collagen production and skin elasticity
- Moisturising skincare: Regular moisturiser and sun protection (SPF 30+) support skin health during and after weight loss
- Medical options: In cases of significant loose skin, your GP can discuss dermatology referral or cosmetic procedures available through the NHS or privately
Track your weight loss progress with our free progress tracker to monitor both your weight and how your skin adapts over time.
- 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 does it take for skin to tighten after weight loss?
This varies significantly. Mild loose skin may improve within 3–6 months as collagen remodels. More significant loose skin may take 1–2 years or longer to partially improve. Younger individuals and those who lose weight gradually typically see better results. Complete resolution without intervention isn't assured, especially after very large weight losses.
Does prescription weight loss medication like Mounjaro or Wegovy cause loose skin?
Weight loss from any source — diet, exercise, or GLP-1 medications like Wegovy — can potentially result in loose skin if weight loss is substantial. The GLP-1 weight loss calculator can help you estimate potential weight loss outcomes. Slower, gradual weight loss minimises this risk regardless of the method used.
Can loose skin be removed without surgery?
Non-surgical options have limited effectiveness for moderate to significant loose skin. Topical treatments, body wraps, and radiofrequency devices marketed for skin tightening show minimal evidence of meaningful results. Significant loose skin typically requires surgical intervention, which your GP can discuss with you.
Is loose skin after weight loss a health concern?
Loose skin itself isn't medically dangerous, though it can increase risk of skin infections in fold areas if not kept dry and clean. The health benefits of weight loss — reduced blood pressure, better blood sugar control, lower cardiovascular disease risk — typically far outweigh concerns about loose skin.
Does drinking more water help skin tighten after weight loss?
Adequate hydration supports overall skin health and collagen function, but won't reverse loose skin on its own. Water intake matters for general health, but tightening loose skin requires collagen remodelling over time, strength training, and sometimes medical intervention. Aim for 6–8 glasses of water daily.
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.