If the car needs to reach Gozo, the route decision is already made: drive to Ċirkewwa and board Gozo Channel. The passenger-only fast ferries do not offer a shortcut for the vehicle.
Buying online is not a sailing reservation
Gozo Channel explicitly says it has no reservation system and boarding is first come, first served. An online ticket can simplify payment, but it cannot promise space on the next departure. Build a buffer into any appointment, flight or last connection.
Check your vehicle class before buying. Standard online vehicle tickets apply to vehicles up to 5.3 metres; larger vehicles require the correct category at the booth. Each passenger in the vehicle also needs an individual ticket for validation at Mġarr.
The round-trip ticket guide explains why validation happens in Gozo. For the current vehicle fare and departure pattern, check the operator and the route board before driving north.