If you're unable to pay off a transferred balance within the given time frame, the balance will begin to accrue interest at the standard APR. To make sure you can pay off the balance in time, divide the balance by the number of months you have to pay it off. For example, if you're working on a balance of $3,000, and the intro balance transfer offer lasts for 18 months, divide 3,000 by 18. As long as you're paying at least $167 monthly, you shouldn't have any issues. However, if you want to be sure, pay a bit more than that.