Fringe benefit tax (FBT) is payable for any whole or part day (24 hour period) a motor vehicle is available for private use.
The default FBT day starts from midnight unless an alternative start time, eg 9am, has been elected. If a vehicle is taken home overnight, it will generally incur two days' FBT.
Example: Default FBT day applies and the motor vehicle isn't used for out-of-town travel
An employee takes a work car home at 6pm for an early start. They return it to their employer’s premises the following day at 2pm. Their employer will have to account for two days’ FBT.
Electing an alternative start time applies to all motor vehicles an employer files an FBT return for. The elected start time will apply for at least two years. In some situations, changes to the alternative start time during the two years may be considered.
Find out more about motor vehicles and an FBT day in IRD's Fringe benefit tax guide (IR409).