User Guide
Using the calculator
The calculator works in three steps. Each screen asks one question — just two sliders and a medicine toggle. Press "Full breakdown →" after step three for the month-by-month receipt and the maintenance question.
Step 1 — How much do you weigh?
Drag the slider to your current weight, or click − and + to nudge it one unit at a time. The unit selector (kg · lb · st) is just below the weight display. Switching units converts the value — your underlying weight doesn't change.
Step 2 — What's your target weight?
Set the weight you want to reach. The target weight turns amber when your reduction would be 15% or more of your starting weight, and red at 25% or more — a prompt to speak with a clinician before setting an aggressive goal. If your target is beyond what clinical evidence suggests the medicine can achieve, the estimate in step three is automatically capped at the drug's practical ceiling.
Step 3 — Your estimate
The central number is the midpoint of your estimated total cost. The range (e.g. £2,100–£2,900) reflects medication price variation across the UK private market: the low end uses P25 (25th-percentile) prices; the high end uses P75 (75th-percentile) prices. Both are calculated over the same midpoint estimated timeline.
The arc of dots represents each month of treatment. Lighter dots are escalation months; full-strength dots are the active weight-loss phase; the final green dot marks the month you're estimated to reach your target.
The pill toggle at the top switches between Mounjaro and Wegovy — the entire estimate recalculates instantly.
The full breakdown
Press "Full breakdown →" from step 3 to open a detailed view with five sections: a month-by-month receipt, a stop-or-maintain card, hidden costs, a note on realism, and an NHS prompt. The month-by-month table shows every real month of treatment — escalation months first, followed by the therapeutic phase.
Stop or maintain?
If you stop: Based on STEP-4 trial data, most patients regain around two-thirds of lost weight within 12 months of stopping. If you maintain: Your estimated monthly cost at the therapeutic dose, and an indicative 5-year figure. There is no recommendation — just the evidence that clinicians use.
Ask your GP about the NHS first
NHS prescribing of GLP-1 medications is available through specialist weight management services for eligible patients. The waiting lists are long but the treatment is free. It is worth asking your GP about referral before committing to private costs.