Calculate the transfer cost first
Most balance transfers charge 3% to 5% upfront. Compare that one-time fee with the interest you would otherwise pay, and confirm how long the introductory APR lasts.
Divide the transferred balance plus fee by the number of promotional months to set a payoff target. Missing the target can expose the remaining balance to a much higher ongoing APR.
Avoid adding new debt
A transfer creates breathing room, not forgiveness. Keep the old account from accumulating a new balance and make every minimum payment on time to preserve promotional terms.