AUS Expat selling home - Question about capital gains tax

[catbus]

We are looking at selling our property in Australia while living in London. We bought the property for around $500,000 4 years ago and the property is no likely to sell for around $700,000 AUD. We are are trying to understand the amount of capital gains tax we will have to pay. We have read about the capital gains withholding for properties over $750k but cannot work out what the effect on CGT is under $750k. Does anyone have any advice on what we can expect to pay in tax? Thanks