Westpac has a good calculator. Banks' online calculators are usually very simplified and can be inaccurate. So before you make any decisions based on them, make sure you talk to the bank or a mortgage broker.
Any potential lender will assess your personal circumstances thoroughly and make you an offer of finance (hopefully!). You may find that they will offer you a lot more than what you are after, or unfortunately, you may not be able to borrow anywhere near the amount of money you want. In some circumstances, you may find it difficult to get any offer of finance at all - if this is the case - your best shot for a home loan may be to contact a mortgage broker for help.
Want to find out more about mortgage brokers? All you need to know is in our mortgage broker guide.