A catch in the new credit reporting system means having an unused credit card limit could now damage your credit score.

That could lead to rejection for loan approval or even a mobile phone contract, even if you pay your bills in full every month.

The average credit limit has jumped to $9143.

Australia is rolling out a comprehensive credit reporting system, with the Treasurer's office releasing draft legislation on Thursday to force the big banks due to join the scheme in July this year. The new system, also called positive credit reporting, gives prospective lenders much more detailed information about consumers' financial habits including their credit limits.

That could be a problem for the large number of Australians who find it prudent to keep a credit card or high credit limit for use in emergencies.