To work out your business use percentage, you need to keep a logbook for your car for a “typical” 12 week period. These must be 12 consecutive weeks (i.e. 12 weeks in a row).
There are very strict ATO rules for completing a car logbook, so make sure you abide by them all. (There’s no sense in doing a logbook, only for it to be deemed worthless by the ATO; get it right the first time and you’re good for five years.)
Your logbook must include every trip you take – not just your business related trips.
The logbook must include the following details:
date for each journey
start and finish times for each journey
start and finish odometer readings for each journey
total number of kilometres for each journey
reason for each journey
start and finish dates for the logbook period
start and finish odometer readings for the logbook period
total number of kilometres travelled during the period
business use percentage for the period