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
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Loose Skin On Arms After Weight Loss: What You Need To Know
Loose skin on the arms is a common concern after significant weight loss, whether through diet, exercise, or prescription weight management medications like Mounjaro or Wegovy. When you lose weight rapidly — particularly more than 1–2 stone — the skin may not have enough time to contract and conform to your new body shape. This happens because skin elasticity depends on collagen and elastin fibres, which stretch during weight gain and may not fully bounce back. Understanding what causes loose skin and what can genuinely help is important for managing expectations after your weight loss 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.
What Causes Loose Skin After Weight Loss?
Loose arm skin develops when the underlying fat layer diminishes but the overlying skin hasn't fully retracted. Several factors influence how much loose skin you might experience:
- Speed of weight loss: gradual weight management (more than 1.5 kg per week) gives skin less time to adapt. The NHS recommends sustainable loss of 0.5–1 kg weekly to support skin elasticity.
- Age: Younger skin has more collagen and elastin, making it more resilient. As you age, these proteins naturally decline, so skin may not tighten as effectively.
- Amount of weight lost: Losing 10–15% of body weight (typically 5–7 kg for most UK adults) has minimal loose skin risk. Losing 20%+ significantly increases the likelihood.
- Genetics: Your family history largely determines how well your skin will contract — this is one factor you cannot control.
- Skin hydration and care: Well-hydrated skin with good sun protection tends to maintain better elasticity over time.
When using prescription weight management medication like Mounjaro or Wegovy, weight loss happens over several months at a measured pace, which may reduce loose skin risk compared to very rapid loss. Our GLP-1 weight loss calculator can help you understand potential weight loss timelines with medication.
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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.
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Strategies That May Help With Loose Skin
Strength and resistance training is one of the most evidence-backed approaches. Building muscle beneath loose skin can help "fill out" the area and improve overall arm appearance and strength. Aim for 2–3 sessions weekly, including exercises like push-ups, tricep dips, and weight-bearing movements.
Skincare and hydration: Keeping skin well-moisturised with quality creams and drinking adequate water supports skin health, though it won't eliminate loose skin. Retinol and vitamin C products may provide modest improvements in skin texture over months.
Time: Skin can continue to tighten naturally for 1–2 years after weight loss. Many people see gradual improvement without intervention.
Professional treatments like radiofrequency, laser therapy, or microneedling are available privately but cost £500–£3,000+ and have mixed evidence. Surgical arm lift (brachioplasty) is an NHS-funded option only in exceptional cases of severe skin excess affecting function or health.
- 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.
Will loose skin disappear on its own after weight loss?
Skin can naturally tighten over 12–24 months as collagen remodels. However, if weight loss is very significant (over 20% body weight), some loose skin may persist. Age and genetics play major roles — younger people typically see better natural retraction than older adults.
Does building muscle help with loose arm skin?
Yes, resistance training can help significantly. Building tricep and arm muscles adds volume beneath the loose skin, improving appearance and function. Combined with cardiovascular fitness, this is one of the most effective non-surgical approaches supported by evidence.
Can prescription weight loss medication like Mounjaro or Wegovy cause more loose skin?
No — in fact, the opposite may be true. These medications typically support weight loss over 4–6 months, giving skin more time to adapt than very gradual weight management. Slower, sustainable loss generally results in less loose skin than crash dieting.
What's the difference between loose skin and excess fat?
Loose skin is actual stretched skin tissue with reduced elasticity. Excess fat is adipose tissue underneath. You can assess the difference by pinching the arm — if it's mostly tissue with minimal fat underneath, it's loose skin; if there's still significant fat, further weight loss may help.
Should I consider arm lift surgery on the NHS?
Arm lift (brachioplasty) is rarely funded by NHS unless loose skin affects function, hygiene, or health. Private surgery costs £3,500–£7,000+. Discuss with your GP if you're considering surgery — they can advise on NHS eligibility and refer you if appropriate.
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.