The Australian Securities & Investments Commission (ASIC) has a very straightforward question on the eve of the Christmas buying rush: "Does your credit card behave like an untrained dog?"

The behavioral pattern of an untrained credit card is clear, according to the commission. It chases after shopping opportunities, chews up your savings with interest charges, and makes a mess of your financial plans. "Like dogs, credit cards must be trained to become enjoyable companions; otherwise they can turn into uncontrollable beasts."

ASIC says the number one sign of an uncontrollable credit card is when the owner makes only the minimum monthly payments required by the lender. The commission points out that making a minimum payment each month can transform a $1000 bill into an 11-year loan, based on certain assumptions. This is almost unbelievable. (See: http://www.fido.gov.au/fido/fido.nsf/byHeadline/Training%20your%20credit%20card)

Here is another piece of almost unbelievable data about wild credit cards: A $10,000 loan can turn into a 27-year loan if only the minimum is paid each month.

These figures should be sobering as Christmas approaches - particularly if you are using multiple credit cards.

One of the great ways to beat the system with a credit card is to ensure that every cent of your debt is paid each month. Sounds tough, but you should appreciate it in the end.

Other looming dangers with Christmas buying in particular are the store promotions offering long interest-free terms. I have heard of interest-free periods of up to five years.

Here's a telling question: Why makes you think that you will have the money in five years if you don't have it now? And in the years until payment is due, there is the very real danger of adding to your debts with more costly purchases.

Another danger is that the lure of long interest-free terms is likely to encourage buyers to give less attention than otherwise to the actual price being paid for a product.