The main concern with buying your new home before you sell the old one is that you’ll own two houses at once and therefore have two loans at once. This works if you have plenty of income to afford the two loans but most people don’t.
Many people’s first thought is to obtain bridging finance however these types of loans can be expensive.
Some banks will allow you to temporarily have the higher loan on both properties until you sell the old home. You’ll need to look at the details of under what conditions the bank will allow this. For example will they want an unconditional contract of sale on the old home before they will allow this.
With this temporarily higher loan you may have higher repayments but there is also the potential to arrange repayments to be the long term amount and have the extra repayment taken from the settlement of the old home.