A balance transfer moves debt from one card to another at a lower promotional rate for a defined period. It is a genuine tool and a genuine trap, depending on what happens before the period ends.
The offer buys time, not relief
The debt is not reduced by the transfer. The same principal moves to a new account where interest accrues at a lower rate, or at none, for a stated window.
Every unit of payment during that window therefore reduces principal rather than servicing interest, which is where the benefit comes from.
If the balance is not cleared before the window closes, the remainder reverts to a standard rate that is usually no better than the original.
The transfer fee is an immediate cost
Most offers charge a fee calculated on the amount transferred, and that fee is added to the balance on day one.
A short promotional period paired with a large fee can produce a worse outcome than staying put, since the fee is certain while the saving depends on clearing the balance in time.
Comparing offers means comparing the fee against the interest that would otherwise accrue over the same window, rather than comparing headline rates.
New spending complicates the account
Purchases made on the transfer card usually attract the standard purchase rate rather than the promotional one, so the account holds balances at two different rates.
Payment allocation rules determine which balance is reduced first. Where regulation requires the highest-rate balance to be paid first, this is manageable.
Where it does not, payments can be applied to the promotional balance while the expensive purchase balance grows untouched, which quietly reverses the benefit.
The credit file reacts in both directions
Opening a new account produces a search and reduces the average age of accounts, both of which tend to weigh slightly against a score in the short term.
The new limit increases total available credit and lowers the overall balance-to-limit ratio, which usually works in the opposite direction and often dominates.
Closing the emptied original account removes that limit again, which can undo the improvement, so the decision to close deserves more thought than it usually gets.
The underlying behaviour decides the outcome
A transfer works where the balance arose from a specific event and the household can clear it within the window on a defined schedule.
It works badly where the original card is used again, since the result is two balances rather than one and a larger total obligation.
Repeated transfers are a signal worth taking seriously, because each one buys time without addressing the gap between income and spending that produced the balance.