The Deferred Interest Trap

"No interest if paid in full" sounds like a free loan — and it is, exactly until it isn't. With deferred interest, the clock is always running: the lender silently accrues interest at the regular APR from the day you buy, and waives it only if you clear the entire promotional balance by the deadline. Miss it by even one dollar, and every month of that accrued interest lands on your bill at once — retroactive from the purchase date, not from the deadline. A $2,000 purchase with a $150 monthly payment still leaves $200 at month 12, and the retroactive interest can add several hundred dollars in a single charge. Always pay more than the minimum, and set the payoff date as your deadline, not the statement date.