ASIC MoneySmart has a calculator to assist you with your decision making process.
This calculator helps you work out how much you need to repay to avoid incurring a high interest rate on the amount still owing and the total cost of the interest-free deal, including fees (if you pay it off within the interest-free period).
Only get an interest-free deal if you can pay more than the minimum each month, are familiar with budgeting and can afford the higher repayment shown using the calculator.
An interest-free deal might not be a good idea if you can only make minimum repayments, have other ways to pay (e.g. savings or lay-by) or have other debts you're struggling to pay off.
Money Smart Interest Free Calculator