Credit card tricks and traps
Differences in the way interest on credit card balances is calculated can cost consumers big dollars. Consumer group Choice found that two consumers with exactly the same transaction history and exactly the same outstanding balance of $2,000 could be paying either $10 in interest or $45, depending on which card they are using.
If you on day late or pay less than the minimum required repayment, most cards will charge you a full rate of interest on the full balance going back to the date of the original transactions, with no interest free days applying. If you fail to pay your bill on time, most cards will not give you any interest free days on new purchases either.
Source: The Age