How a transfer really works
A new card pays off your old card, and you owe the new card instead. You usually pay a one-off fee of 3% to 5% of the amount moved, added to the new balance. Then the balance sits at a promotional rate, often 0%, for a set number of months. In September 2026 the longest common offers ran for 21 months. After that, whatever is left is charged the card's normal rate.
The number that matters
Divide the balance plus the fee by the number of promo months. That's what you need to pay each month to finish before the promo ends. If you can pay it, a transfer can save a lot. If you can't, the calculator shows what's left when the normal rate kicks in.
Don't confuse it with deferred interest
Store cards and some financing deals say "no interest if paid in full" by a date. That is different. If even a small amount is left when the date passes, interest can be charged all the way back to the purchase date, as the CFPB explains. A 0% balance transfer card charges interest only from when the promo ends.
Where your payments go
If the new card also has purchases on it at a higher rate, federal rules send anything you pay above the minimum to the highest-rate balance first. That helps. Your minimum can still go to the 0% balance, though, so the simplest plan is to put no new purchases on the transfer card at all.
