Mangawhai Heads is about 110 km north of Auckland — around ninety minutes by car when traffic is good, longer in summer. The most direct route is up State Highway 1 to Kaiwaka, then east on the Kaiwaka–Mangawhai road. There are no trains or scheduled bus services to the Heads, so you need your own car or a rental.
From Whangarei the drive south is about an hour, mostly on State Highway 1 with the same turn-off at Kaiwaka. Fuel up before you leave the highway; there is no service station at the Heads itself.