There really isn't any simple answer because nobody can predict the future of interest rates, not even the Reserve Bank of Australia (RBA).
Firstly, you should decide if it is suitable for you to fix your home loan based on the future plans for your finances and the property that is security for the loan.
When is fixing a bad idea?
A fixed rate home loan works in a very different way to a variable rate home loan. You will lose a lot of the flexibility and may face high exit fees if you make changes to your loan or make extra repayments during the fixed rate period.
Don't fix your loan if:
You need to make large extra repayments on your loan.
You may sell the property that is security for your mortgage.
You may refinance your home loan.
You plan to renovate or build a new home, often you may need to refinance.
You don't like being locked in with a particular lender or loan product.
How long should you fix for?
The longer you fix your loan, the higher the premium you will pay for the security of a fixed interest rate. Most people choose 3 year and 5 year fixed rate loans, so the banks often have specials for these terms.
Most people choose their fixed rate term based on what they believe the future of interest rates will be, and when they expect their circumstances or needs may change, so that they may need to refinance their loan, make a large payment off the loan or sell their property.
You should assess your own future personal needs before you fix your interest rate.