Method
Per-person daily categories — food, local transport, activities, and the misc buffer — are multiplied by the number of days and the number of travellers. Lodging is kept as a shared per-room cost, so it scales with days but not with party size. Flights are added as a per-person one-off. In road-trip mode, fuel is estimated as round-trip distance ÷ efficiency × fuel price, and tolls are added as a single trip total.