What is the ruling on zakat for a passenger transport company that incurs losses at the end of the year?

Zakat (definition) is not obligatory on cars prepared for rent or passenger transport because they are acquired assets, not commercial goods. Zakat becomes obligatory on their rental income if it reaches the nisab (definition) and a full hawl (lunar year) has passed over it, regardless of whether the activity resulted in a profit or a loss. If the rental income does not reach the nisab, or if it falls below it during the hawl, then there is no zakat due on it.