How does a balance transfer credit card actually work?

A balance transfer credit card lets you move existing debt from one or more credit cards onto a new card, typically one offering a low or 0% introductory interest rate for a set period, usually 12 to 21 months. You apply for the new card, request the transfer, and the new card issuer pays off your old balance. You then owe that amount to the new card instead. The goal is to save money on interest while paying down the principal faster. Most cards charge a balance transfer fee of 3 to 5 percent of the amount transferred. If you don't pay off the balance before the promotional period ends, the remaining amount gets hit with the card's regular interest rate, which can be quite high.