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
Stretch Marks Before and After Weight Loss
Stretch marks are a common skin change that can occur both during weight gain and weight loss. When you lose weight—whether through lifestyle changes, exercise, or prescription weight management medication—your skin may not shrink at the same rate, potentially leaving stretch marks or scars. Understanding what causes them, how to prevent them, and when to seek help from your GP is important for your overall health and confidence during your weight loss journey.
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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.
Weight Loss and Stretch Marks: What Causes Them
Stretch marks form when the skin stretches or shrinks rapidly, damaging the collagen and elastin fibres beneath the surface. During significant weight loss, the skin loses elasticity and may not retract evenly, leaving visible marks—typically purple, red, or silver in colour depending on age.
- gradual weight management increases the risk of stretch marks because skin cannot adapt quickly enough
- Age and genetics affect skin elasticity—younger skin typically recovers better
- Hydration and nutrition influence skin health and elasticity during weight loss
- Prescription weight loss medications like Mounjaro and Wegovy can support steady weight loss, which may reduce the risk of severe stretch marks compared to very gradual weight management
The NHS recommends losing weight at a sustainable rate of 0.5–1 kg per week. This gradual approach gives your skin time to adapt and may help minimise stretch mark formation. You can track your weight loss progress using our free progress tracker to monitor your rate of loss and adjust your approach 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.
NHS Weight Loss Options and Skin Changes
If you're considering prescription weight management in the UK, your GP can discuss options including Mounjaro (tirzepatide), Wegovy (semaglutide), or Saxenda (liraglutide) for eligible adults. These prescription medications are used alongside diet and exercise to support sustainable weight loss, which may help your skin adapt better than gradual weight management alone.
Eligibility for NHS weight loss medication requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes or high blood pressure. You can use our free BMI calculator to check your current status, then speak with your GP about referral to specialist weight management services in your area. Private prescriptions are also available following online clinical assessment if NHS waiting lists are long in your region.
- 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.
Do stretch marks go away after weight loss?
Most stretch marks fade over time, changing from red or purple to silver or white. Complete removal is rare, but treatments like laser therapy, microdermabrasion, or topical retinoids may help. Your GP can refer you to dermatology services on the NHS if marks are causing concern. Newer marks typically respond better to treatment than older ones.
Can I prevent stretch marks during weight loss?
Keep skin well hydrated by drinking plenty of water, use moisturisers containing collagen-boosting ingredients, and maintain a diet rich in vitamins C and E. Most importantly, lose weight gradually—the NHS recommends 0.5–1 kg per week. This gives your skin time to adapt. Avoid gradual weight management methods unless under medical supervision.
Are stretch marks worse with weight loss injections like Wegovy or Mounjaro?
No—prescription weight loss medications are designed to support steady, sustainable weight loss when combined with diet and exercise changes. In fact, gradual weight loss may result in fewer or less severe stretch marks compared to gradual weight management. Individual results vary, and skin adaptation depends on genetics, age, and hydration.
When should I see my GP about stretch marks?
Most stretch marks don't require medical attention and fade naturally. However, see your GP if marks are causing distress, are very severe, or if you'd like to discuss treatment options. Your GP can refer you to NHS dermatology services or discuss private treatment options available in the UK.
How can I work out if weight loss medication is right for me?
Check your BMI using our free BMI calculator on this page, then discuss the results with your GP. They can assess whether you're eligible for NHS specialist weight management services or prescription medication. Eligibility depends on BMI and any weight-related health conditions. A prescriber will review your full health history before recommending treatment.
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.