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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Weight Loss By Date Calculator — UK Prescription Options
Planning your weight loss journey requires realistic expectations and the right support. If you're looking to lose weight by a specific date in the UK, prescription weight management medications like Mounjaro and Wegovy may help—but only if you're eligible. This guide explains how these medications work, what weight loss you might expect from clinical evidence, and how to access them through the NHS or private prescribing. Everyone's results vary, so it's essential to understand both the potential benefits and the commitment involved.
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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.
UK-Licensed Prescription Weight Loss Medications
Three prescription medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — A once-weekly dual GIP and GLP-1 agonist injection. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks when combined with a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. Clinical trial data showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — A daily GLP-1 injection, less commonly prescribed than Mounjaro or Wegovy.
All three are prescription-only medicines requiring a clinical assessment. You'll need a BMI of 30 or above, or 27–29.9 with weight-related health conditions (such as type 2 diabetes or high blood pressure) to be eligible. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply. Individual results with prescription weight loss medication vary significantly—these figures are clinical averages, not assures.
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.
Accessing Weight Loss Medication: NHS vs Private
NHS Route: Weight loss medications are available through specialist tier 3 weight management services. You'll need a GP referral, and availability varies considerably by region. Waiting times can range from several months to over a year in some areas.
Private Route: GPhC-registered online pharmacies offer prescription weight loss treatment following an online clinical assessment with a UK-licensed prescriber. This route typically has shorter waiting times but involves a cost (roughly £129–£320 per month depending on dose).
Whichever route you choose, use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to check your starting point. Your GP can advise on NHS eligibility and discuss whether prescription medication is right 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 lose weight by a specific date using prescription medication?
Weight loss timelines vary greatly between individuals based on starting weight, dose, adherence, and lifestyle factors. Clinical trials show average results, but individual outcomes differ. Mounjaro and Wegovy typically require 12–16 weeks to reach an effective maintenance dose, so realistic planning is essential. Your prescriber can discuss realistic expectations.
Am I eligible for NHS weight loss medication?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with a weight-related health condition like type 2 diabetes, high blood pressure, or sleep apnoea. South Asian and Black African/Caribbean adults may be eligible at lower BMI thresholds. Ask your GP about referral to specialist weight management services.
How quickly will I lose weight on Mounjaro or Wegovy?
Both medications require gradual dose increases over weeks before reaching maintenance dose. Weight loss typically becomes noticeable after 4–8 weeks on an effective dose. Average loss is 0.5–1.5 kg per week depending on the individual, diet, and exercise. Everyone's timeline is different.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), while Wegovy (semaglutide) activates one (GLP-1). Mounjaro users averaged slightly higher weight loss in trials (up to 21% vs 15%), but results vary individually. Both are once-weekly injections requiring prescription.
Will I keep the weight off after stopping medication?
Weight loss medications work best alongside lasting lifestyle changes. Without continued medication, diet, and exercise, some weight regain is common—as it is with any weight loss approach. Long-term success depends on maintaining healthy habits beyond the medication period.
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.