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
Will Eating Less Cause Weight Loss?
Yes, eating less does cause weight loss — but the relationship between food intake and weight loss is more nuanced than simple math. A calorie deficit (consuming fewer calories than your body burns) is the fundamental requirement for sustainable weight loss. However, factors like metabolism, diet quality, physical activity, and individual health conditions all influence how effectively eating less translates to actual weight loss. The NHS recommends a gradual, sustainable approach rather than extreme restriction, and understanding the mechanisms behind weight loss can help you achieve lasting results.
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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.
How Calorie Deficit Works for Weight Loss
Weight loss occurs when you consume fewer calories than your body expends — this is called a calorie deficit. The NHS recommends creating a deficit of around 500 calories per day, which typically results in losing approximately 0.5 to 1 kg per week. This is considered safe, sustainable weight loss.
However, simply eating less does not clinically studied weight loss if the total calorie intake is still too high. For example, eating smaller portions of high-calorie foods may not create sufficient deficit. Diet quality matters: protein-rich foods, whole grains, and fibre help you feel fuller longer, making a calorie deficit more maintainable.
- Eating less without moving more: calorie deficit still occurs
- Eating less with increased activity: larger deficit, faster weight loss
- Extreme restriction (very low calorie diets): may cause muscle loss and nutrient deficiency — requires medical supervision
- Moderate, consistent deficit: most sustainable long-term approach
Your basal metabolic rate (BMR) — calories burned at rest — varies by age, sex, weight, and muscle mass. This is why two people eating the same amount may lose weight at different rates. Use our free weight converter and BMI calculator to understand your current position, then calculate a realistic calorie target with your GP or a registered dietitian.
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.
When Eating Less Alone May Not Be Enough
For some people, eating less does not produce expected weight loss despite maintaining a calorie deficit. This can be due to medical conditions (thyroid problems, polycystic ovary syndrome, type 2 diabetes), medications that affect metabolism, or genetic factors affecting hunger hormones.
In these cases, prescription weight loss medication may be recommended alongside dietary changes. GLP-1 medications like Wegovy (semaglutide) and Mounjaro (tirzepatide) are licensed for weight management in UK adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. These are prescription-only medicines that work alongside eating less and increased activity — they do not replace dietary changes. Evidence from clinical trials shows these medications support weight loss when combined with reduced-calorie intake and physical activity. Try our free GLP-1 weight loss calculator to estimate potential results, and discuss prescription options with your GP if appropriate.
- 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.
How much should I eat per day to lose weight?
The amount varies by your current weight, age, sex, and activity level. As a guide, the NHS suggests a calorie deficit of around 500 calories daily for gradual weight loss. A registered dietitian or your GP can calculate your personalised target. Use our BMI calculator above to establish your current baseline.
Will I lose weight if I eat less but do not exercise?
Yes. A calorie deficit from eating less alone does cause weight loss. However, combining eating less with physical activity produces faster results and helps preserve muscle mass. Exercise also supports cardiovascular health and mental wellbeing alongside weight management.
How quickly will I lose weight by eating less?
The NHS recommends aiming for 0.5 to 1 kg per weight loss per week, achieved through a 500-calorie daily deficit. Results vary based on your starting weight, metabolism, and diet consistency. Faster weight loss is possible but increases the risk of muscle loss and nutrient deficiency.
Does the type of food matter if I eat less overall?
Yes. Eating less of high-calorie, low-nutrition foods is less effective than eating smaller portions of nutrient-dense foods. Protein, whole grains, and fibre support satiety (feeling fuller), making a calorie deficit easier to maintain long-term than restriction alone.
When should I consider weight loss medication if eating less is not working?
If you have maintained a calorie deficit for several months without expected weight loss, discuss with your GP. Prescription weight loss medications are available in the UK for eligible adults. Your GP can assess whether medication might support your weight management alongside dietary changes.
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.