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
Weight Loss on 5:2 with UK Prescription Medication
The 5:2 diet combined with prescription weight management medication may offer an effective approach for UK adults seeking sustained weight loss. Many people find that fasting on 5:2 works better when supported by medical options like Mounjaro or Wegovy, which help reduce appetite and support feeling fuller. Our GLP-1 weight loss calculator can show you projected results, and your GP can advise whether combining these approaches is suitable for your individual health circumstances.
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.
UK-Licensed Weight Loss Medications Available
Several prescription-only medications are now available in the UK for weight management and may complement a 5:2 fasting approach:
- Mounjaro (tirzepatide) — a once-weekly dual GIP/GLP-1 receptor agonist injection. Clinical trials showed participants lost an average of 15–21% of their body weight, though individual results vary significantly.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. In clinical trials, participants achieved approximately 15% average weight loss over 68 weeks alongside reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a daily GLP-1 injection, offering an alternative for those who prefer daily dosing.
All three are prescription-only and require a clinical assessment to determine eligibility. UK eligibility generally includes adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea.
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.
NHS vs Private Access — How to Find Out Your Options
NHS access: Available through specialist tier 3 weight management services, typically accessed via GP referral. NHS services vary significantly by region and waiting times can be lengthy in many areas.
Private access: Available through GPhC-registered online pharmacies following a remote clinical assessment with a UK-licensed prescriber. This route does not require NHS referral and often offers faster access.
Use our free BMI calculator above to check whether you may fall within eligibility thresholds, then speak with your GP about whether prescription medication alongside 5:2 fasting is appropriate for your health situation.
- 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.
Can I combine 5:2 fasting with weight loss injections like Mounjaro?
Many people do combine 5:2 fasting with prescription weight loss medication, as GLP-1 medications help reduce appetite and may support feeling fuller on fewer calories. However, you should discuss this approach with your prescriber or GP before starting, as they can advise whether it is safe and appropriate for your individual health circumstances.
How long does Mounjaro or Wegovy take to show weight loss results?
Results vary between individuals. Clinical trials showed measurable weight loss typically began within the first 4–8 weeks, with more substantial loss by 12–16 weeks. However, some people see changes faster or slower. Individual results vary significantly, and medications work best alongside reduced-calorie diet and increased physical activity.
Will the NHS prescribe weight loss injections on the 5:2 diet?
NHS prescription of weight loss medication depends on your BMI, health conditions, and local NHS availability. Eligibility generally requires BMI ≥30 or BMI 27–29.9 with comorbidities. Your GP can assess whether you qualify and refer you to specialist weight management services if appropriate.
What happens to weight if I stop taking Wegovy or Mounjaro?
Weight loss achieved with GLP-1 medications is typically sustained by ongoing lifestyle changes including diet and physical activity. If you stop the medication without maintaining these changes, weight may return over time. This is why pairing medication with approaches like 5:2 fasting may help create sustainable habits.
Is it safe to do 5:2 fasting while taking weight loss medication?
This varies by individual and medication. Some people find very low calorie days on 5:2 may cause side effects like nausea when combined with GLP-1 medications. Always discuss your specific fasting plan with your prescriber or GP before starting, as they can advise on safe calorie targets and monitoring for your situation.
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.