Having a bigger deposit puts you in a better negotiating position, regardless of what type of interest rate you're choosing. With a 20% deposit means you should be able to avoid paying Lender's Mortgage Insurance (LMI), and get a competitive interest rate. Having a deposit of even more than 20% puts you in a definitely less risky category from the lender's viewpoint, and you should be able to negotiate a truly competitive rate if all your other financial factors (income, total debt, credit score) are sound. Having a bigger deposit may help if you want to negotiate a longer fixed term, but it will probably not have a major impact on this feature of your loan.