Australians will put about $400 million on their credit cards, with about 60 per cent of sale buys to be charged to plastic.

This equates to $213 for each of the 18.7 million Australians who have credit cards, totalling $399 million, according to Lonergan Research.

The survey of 1038 people, aged over 18 from regional and metropolitan areas, found 21 per cent of people almost always use their credit card to buy a big-ticket item.

More will go on Gen Y's credit cards compared to other generations, while men plan to spend an average of $433 in the sales.

This is considerably more than women, who plan to spend only $281.

On a state by state basis, NSW residents intend to spend the least in the sales, at $288, while people in the resources-rich Western Australia will spent the most at $463.

More than 14.5 million people don't know the interest rate that may apply to the sales purchases.

Vittoria Shortt (Shortt), chief executive of Bankwest Retail, which commissioned the research, urged caution when choosing a card.

"We all love the buzz of a bargain, but our research suggests many Australian shoppers may end up paying more for their bargains than they intend to," she said in a statement on Sunday.

"We're urging sale shoppers to get to know their interest rate.

"Choosing a card with a long-term low purchase rate means that a splurge in the sales can still represent good value even if the card holder chooses to pay this item off over a number of months."