I'd recommend that you rent your old house if you can - this also gives you the option to move back there if your circumstances change. You can use it as equity to help you get a loan for a Sydney place too - I suggest you talk to an accountant who specialises in these things. I've met many people who recommend never selling a property once you buy it and I hope to follow that advice when we get a place of our own. The tax laws seem to benefit those who do this but it's good to be informed.