Instant BMI calculation + NHS vs private thresholds explained. Find out if you qualify in under 30 seconds.
BMI still matters for Mounjaro eligibility—whether you're trying to access it via NHS or private prescription. But the thresholds differ, and "maintenance BMI" rules add another layer of confusion. This page gives you instant answers with our UK-specific calculator, plus clear explanations of what your result actually means.
Use our interactive calculator below to find your BMI and see instant eligibility guidance for both NHS and private Mounjaro access.
Understanding the different BMI requirements is crucial for knowing which route (NHS or private) is realistic for you.
| Criteria | NHS Route | Private Route |
|---|---|---|
| Starting BMI | ≥35 with comorbidity OR ≥40 without |
Typically ≥30 (Some accept ≥27 with conditions) |
| Maintenance BMI | Must maintain 5% loss at 6 months | Varies by provider (often ≥20-25) |
| Comorbidities Required | Yes (for BMI 35-39.9) | No (but may help at lower BMIs) |
| Waiting Time | 3-6 months (referral to prescription) | 1-2 weeks |
| Monthly Cost | ~£9.90 (prescription fee) | £150-£400+ depending on dose |
BMI is a useful screening tool, but it has significant limitations when it comes to individual health assessment:
💡 Clinical Decision:
BMI is a starting point, not the final word. Private prescribers and NHS specialists assess your individual circumstances holistically. If you're borderline, factors like comorbidities, previous weight loss efforts, and overall health can make the difference.
One of the most confusing aspects of Mounjaro access is "maintenance BMI" – what happens if your BMI drops below the starting threshold?
You start Mounjaro at BMI 32. Six months later, you've lost 15% of your body weight and your BMI is now 27. Can you continue treatment?
Answer: It depends on your provider.
| Provider Type | Maintenance Policy |
|---|---|
| Maintenance-Friendly | Accept patients with BMI ≥20-25 if already on treatment |
| Strict Threshold | Require you to maintain BMI ≥30 at all times |
| Case-by-Case | Assess individually based on medical need |
Our advice: If you're planning long-term Mounjaro use (6+ months), start with a maintenance-friendly provider to avoid forced switching later.
Download our printable BMI tracking sheet to monitor your progress over time. Includes:
Format: PDF (A4, printable) | Cost: Free, no signup required
Private: Most providers require BMI ≥30, though some accept ≥27 if you have weight-related health conditions (PCOS, prediabetes, high blood pressure). NHS: You need BMI ≥35 with at least one comorbidity, OR BMI ≥40 without other conditions. NHS access is much more restrictive and currently limited to specialist weight management services.
No – BMI calculation is standardized (weight in kg ÷ height in m²). However, pharmacies apply different BMI thresholds for eligibility. Some accept BMI 27 with conditions, others require 30 minimum. The confusion comes from varying policies on maintenance BMI (what BMI you can drop to while continuing treatment). Always check the specific provider's criteria before completing an assessment.
New patients: Very difficult. A few private providers may consider BMI 27-30 if you have significant weight-related health conditions, but this is rare and requires individual medical assessment. Maintenance patients: Yes, some providers accept BMI 20-25 if you're already established on treatment and losing weight successfully. Check our maintenance-friendly providers list for specific options.
It depends on your provider's maintenance policy. Maintenance-friendly providers: Will continue prescribing even if your BMI drops to 20-25 (the whole point is you're losing weight!). Strict-threshold providers: May refuse to continue if you drop below BMI 30, even if you're benefiting from treatment. This is why choosing a maintenance-friendly provider from the start is crucial if you're planning long-term use. The NHS allows continuation below starting BMI if you've achieved ≥5% weight loss and continue to benefit medically.
The calculation is the same, but health risk thresholds differ. For people of South Asian, Chinese, or Black African/Caribbean descent, health risks associated with excess weight begin at lower BMI values. For example, a South Asian person with BMI 27 may have similar health risks to a white European person with BMI 30. Some clinicians adjust thresholds accordingly when assessing Mounjaro suitability, but this is at individual provider discretion. If you're from an at-risk ethnic group with BMI 27-30, mention this in your assessment as it may support your case.
If you're BMI 27-30: (1) Check if you have weight-related conditions (PCOS, prediabetes, high BP, sleep issues) – these strengthen your case. (2) Look for providers who accept lower BMIs with comorbidities. (3) Consider asking your GP for a formal weight-related health assessment to document conditions. (4) If declined, you may need to explore other options (lifestyle changes, alternative medications) or reassess in future. Don't artificially inflate weight before assessment – providers may require stable weight history.
Already on Mounjaro? See maintenance-friendly providers
Maintenance Providers →This guide is regularly reviewed. Here's what's changed recently in the UK:
This BMI calculator is for informational purposes only and does not constitute medical advice. BMI is a screening tool with limitations and should not be the sole factor in health decisions. Mounjaro (tirzepatide) is a prescription-only medication in the UK. Eligibility is determined by qualified healthcare professionals based on individual medical assessment, not BMI alone. The thresholds provided represent general guidelines – actual prescribing decisions consider multiple factors including comorbidities, previous weight loss attempts, and overall health. Always consult a GMC-registered doctor or GPhC-registered pharmacist for personalized medical advice. See our full medical disclaimer.
Our BMI calculator uses the standard WHO formula. Eligibility thresholds are based on current UK provider policies, NHS NICE guidelines, and MHRA regulations as of 2026.
