There are a host of good calculators already available on the web. I suggest that you avoid using lenders “how much can I borrow” calculators as these are very approximate and can lead to severe disappointment.
A good mortgage broker will always use the lender’s real servicing calculator to ensure that you will get the approval that you want and avoid those unnecessary failed inquiries on your credit report.
A good set of calculators are available at http://www.peachhomeloans.com.au/calculators.htm