Why should you be cautious of no-interest offers on credit cards?

Many retailers promote credit cards with a zero-percent amount of time. These cards allow you to buy big-ticket items, without paying interest for anywhere from six months to more than a year. With many of these offers, you must pay off the entire purchase by the time the promotional period ends to take advantage of the zero-rate offer. If you dont, the lender will charge you interest from the date you bought the item. You would then have to pay interest  at the lenders standard rate  from the date of purchase. And if the Annual Percentage Rate or APR on the retailers card is higher than what you would pay on another card you have, the extra costs could really add up.