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
What Is a Syns Calculator and How Does It Work?
A syns calculator is a tool used primarily within the Slimming World weight loss programme to assign "syn" (synonym) values to foods based on their nutritional content, helping members track daily food intake against a daily syn allowance. Syns are a simplified food tracking system designed to make calorie and nutrient counting more accessible for UK dieters. While syns calculators are useful for structured weight management programmes, they work best alongside broader lifestyle changes including increased physical activity. If you're exploring weight management options in the UK, our free BMI calculator can help you understand your current health status and whether weight loss might be beneficial for your 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.
How Syns Calculators Fit Into Weight Management
Syns calculators assign point values to foods based on calories, fat, and fibre content, allowing users to stay within a daily syn allowance (typically 15–20 syns per day depending on the programme). The system is designed to make healthy eating more flexible by allowing a variety of foods within the daily limit, rather than restricting specific food groups entirely.
- Food tracking: Users input foods consumed and the calculator totals daily syns
- Personalised allowances: Different programme versions offer different daily syn targets
- Flexibility: Syns allow for treats and less healthy foods within daily limits, supporting adherence
- Behaviour change: Regular tracking encourages awareness of food choices and portion sizes
Syns calculators are most effective when combined with physical activity, realistic calorie targets, and sustainable eating habits. Evidence suggests that structured food tracking programmes contribute to modest, sustainable weight loss when users are engaged and consistent.
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.
Syns Calculators vs. Other Weight Loss Tools
Syns calculators are one of several approaches to weight management available in the UK. Other methods include simple calorie counting (using kcal targets), NHS Healthy Weight guidance (based on BMI and balanced nutrition), and prescription weight management options for eligible adults.
- Calorie counting: Direct tracking of kilocalories — more precise but potentially less flexible
- NHS guidance: Focus on balanced portions and food types rather than point systems
- Medical interventions: For eligible adults, GLP-1 weight management medications (such as Mounjaro or Wegovy) may be prescribed alongside lifestyle changes
The best approach depends on individual preference, lifestyle, and medical circumstances. Our free weight converter helps you track progress in your preferred units (stone, kg, or lbs), and our GLP-1 weight loss calculator can estimate potential outcomes if prescription medication eligibility is being considered.
- 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.
Are syns calculators accurate?
Syns calculators are reasonably accurate if food entries are logged correctly. However, accuracy depends on portion size estimation and the database of food values within the calculator. For precise medical or dietary guidance, consulting your GP or a registered dietitian is recommended.
Can I use a syns calculator to lose weight?
Yes, syns calculators can support weight loss when used consistently alongside a calorie deficit and physical activity. The NHS recommends aiming for 0.5–1 kg per week weight loss for sustainable results. Tracking tools like syns calculators help with accountability and awareness.
How many syns should I have per day?
Typical daily syn allowances are 15–20 syns, though this varies by individual circumstances, programme version, and starting weight. The Slimming World programme provides personalised guidance. Always follow the programme guidelines or speak to your GP for medical advice.
Do syns calculators work better than calorie counting?
Neither is inherently superior — the best tool is the one you'll use consistently. Syns calculators offer flexibility and structure, while calorie counting is more precise. Our free BMI calculator can help you assess your current weight status and whether structured tracking might benefit you.
Are prescription weight loss options available alongside syns tracking?
Adults in the UK with a BMI of 30 or above (or 27+ with weight-related conditions) may be eligible for prescription weight management medication through NHS specialist services or private prescribing, used alongside lifestyle changes and healthy eating programmes.
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.