How do I buy a house if I need to sell my house for the deposit?

You may be able to use a Bridging Loan if you have enough equity in your existing home i.e. where the value of your current home is higher than the existing loan attached to the home. A Bridging loan may allow you to borrow the full amount of the new property value plus costs to purchase the new property while retaining the existing property and existing debt. Then once you sell your existing property you payout enough debt to make sure the loan to value ratio of the remaining loan amount against the new property is acceptable to the Lender. Be careful though because Bridging loans are more expensive than normal loans (1% to 2% possibly) are are for short term use only so you want to make sure you will be able to sell your existing loan within a set period after settling on your new property and moving in. Another option is to negotiate with the Vendor of the property you want to purchase to get an extended settlement date. You could negotiate a 6 month settlement leaving you ample time to sell your new property before you settle on your existing property. NOTE: not all Vendors will be willing to negotiate this extension especially given the standard settlement period in Sydney is 6 weeks.