Claiming Mileage on my Tax Return?

Well of course there is the obvious choice of using the cents per km method where you don't need to substantiate with any logbook etc but you can only claim up to the 5000km and nothing more and you'd use the cents prescribed by the ATO based on the size of the engine. You should still keep some sort of journal entry noting its use although you probably won't be hassled about it. If you wanted to claim the vehicle expenses (for travel over 5000km) instead such as oil, maintenance etc you would have to keep all the receipts but you would only be able to claim 1/3 of the total vehicle expenses, check with the ATO's website on what car expenses are allowable. Only if you had a logbook could you claim almost all of it if you are using it primarily for work. Note though that these methods are mutually exclusive so you can only use one per year.