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
Why Has My Weight Loss Slowed on Mounjaro?
If your weight loss has plateaued after starting Mounjaro, you're not alone. Weight loss on this weekly weight loss injection typically follows a pattern: faster initial loss, then a slower, more sustainable phase. This is normal and expected. Your prescriber may adjust your dose, or changes to your diet and activity level might help restart progress. Understanding what's happening and when to seek GP support is key to managing your weight loss journey effectively.
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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 Weight Loss Plateaus on Mounjaro
Weight loss on Mounjaro (tirzepatide) typically follows three distinct phases. In the first 4–8 weeks, you may experience rapid initial weight loss as your body adapts to reduced appetite and food intake. After 8–16 weeks, the rate of weight loss usually slows and becomes more gradual — this is a natural adaptation as your body reaches a new equilibrium. By weeks 16–20, many people experience a plateau where weight loss stalls completely, even though they're following their diet and exercise plan.
This plateau happens for several reasons. Your body becomes more efficient at the lower calorie intake (metabolic adaptation). Mounjaro's appetite-suppressing effects may lessen slightly over time as your body adjusts to the medication. Additionally, as you lose weight, your total daily calorie needs decrease, so the same deficit no longer produces the same weight loss rate. This is not a sign that Mounjaro has stopped working — it reflects normal physiological responses to sustained weight loss.
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.
What You Can Do If Weight Loss Has Slowed
If you've hit a plateau, several evidence-based approaches may help. First, review your diet and activity level with your GP or a registered dietitian. Small increases in physical activity or adjustments to calorie intake can restart progress. Second, your prescriber may recommend dose titration — increasing your Mounjaro dose if you haven't reached the maximum 15 mg weekly injection yet. Many people find that moving to the next dose level reignites weight loss. Third, ensure you're taking your KwikPen injection consistently each week and storing it correctly (2–8°C unopened, below 30°C after first use for up to 30 days). Try our free GLP-1 weight loss calculator to project potential outcomes at different doses. Finally, be patient — sustainable weight loss often involves plateaus, and restarting progress may take 4–6 weeks after a change.
- 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.
Is a weight loss plateau on Mounjaro normal?
Yes, completely normal. Weight loss typically follows a pattern: rapid initial loss, then gradual slower loss, then plateaus. This reflects your body adapting to lower calorie intake and the medication's effects stabilising. Plateaus lasting weeks are common and do not mean the medication has stopped working.
Should I increase my Mounjaro dose if weight loss has slowed?
Only your GP or prescriber can recommend a dose increase. If you haven't reached the maximum 15 mg weekly dose, your prescriber may suggest escalation after assessing your response. Dose increases usually happen every 4 weeks minimum. Never adjust your dose without medical guidance.
Can I restart weight loss without increasing my dose?
Yes. Review your calorie intake and physical activity with your GP or dietitian. Even small increases in activity or modest dietary adjustments can restart progress. Some people find that consistency over 4–6 weeks reignites weight loss without needing a higher dose.
How long should I wait before contacting my GP about a plateau?
If weight loss has completely stalled for more than 4–6 weeks despite consistent diet, exercise, and medication use, contact your GP. They can review your progress, assess whether a dose increase is appropriate, and rule out any underlying health factors affecting weight loss.
Does my calorie intake need to change as I lose weight on Mounjaro?
Yes. As you lose weight, your body requires fewer total calories daily. A deficit that produced 0.5 kg/week loss at your starting weight may produce less loss at a lower weight. Your GP or dietitian can help recalculate your calorie needs and adjust your target intake accordingly.
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.