You don't have to physically change it anywhere, it just becomes an investment property by nature of the fact that you have probably moved out of it and put a tenant in.  Important things to do are to note the date it all happens, keep good records suchas spreadsheets, tenancy agreements etc FOREVER.  You can be audited by the tax office for up to ten years (or longer if they suspect fraud). I say forever, as you might for example keep the property for 20 years say and rent it out the majority of that time.  You will need every receipt, rate notice etc after from that time to work out the capital gains, and accurate records gives you the figures to ascertain your cost base.  Also it's imperative to obtain a valuation as soon as possible – the higher the valuation at change date or thereabouts the better for you later when it comes to working out capital gains tax if you sell for example as the amounts that matter are the value at the date of change and the sell price and date, if this is what occurs.  The capital gains tax will be based 50% of the difference, so the less the difference the better if you get the drift.  ATO has some good free booklet publications they can send if you ring their number and request them.