A balance transfer credit card allows you to transfer existing credit card balances to a new card with a lower interest rate, sometimes even 0%, for a set period. It is important to choose a card with a long enough 0% period to pay off the balance and not spend on the card, as new purchases will accrue interest until the transferred balance is paid. The best cards offer 0% interest for 12-24 months on transfers and a regular purchase rate under 10%.