See how much interest you could save by transferring a balance to a lower-rate card, after transfer fees.
A balance transfer moves debt from a high-rate card or loan to a lower-rate one, usually for a fee. The saving is real, but it is not the difference between the two rates — it is the interest avoided over the period you will actually take to repay, minus the transfer fee, and minus whatever the rate reverts to once any promotional window ends. Those three adjustments are where most of the apparent benefit disappears.
So the calculation that matters is a break-even one. Work out the interest you would pay on the existing balance over your realistic repayment period, then the interest on the new one including the fee, and compare totals rather than rates. Two traps are worth naming. A promotional rate that expires while a balance remains can leave you worse off if the reverting rate is high. And a transfer that frees up the old card without a change in spending habits frequently ends with two balances instead of one, which is the most common way this goes wrong.
Compare total interest, not rates. Work out what you would pay on the current balance over your realistic repayment period, then the same on the new one with the transfer fee added. If the second total is meaningfully lower, it is worth doing.
Any remaining balance moves to the standard rate, which is often high. If you cannot clear the balance within the promotional window, include the reverting rate in your calculation or the transfer may cost more than it saves.
It can move in both directions. A new account and the associated enquiry may lower it slightly at first, while reduced utilisation on the old card can help. The larger long-term factor is whether the transfer actually helps you clear the debt.
Not automatically. Closing it removes available credit and can raise your overall utilisation ratio, and closing a long-held account shortens your credit history. The real risk is not the open card but running the balance back up on it.