Balance Transfer Calculator

How balance transfers work — and when they make sense

A balance transfer lets you move existing credit card debt to a new card offering 0% interest for a promotional period — typically 12 to 30 months. During that window, every pound you pay reduces the principal directly. No interest. On a £3,500 balance at 24.9% APR, that alone is worth several hundred pounds.

How balance transfers work

You apply for a new balance transfer card and, once approved, instruct the new provider to pay off your old card. The debt moves across and you owe the new provider instead. A one-off transfer fee — usually 1–3.9% of the balance — is charged upfront. So on £3,500 at 3%, you'd owe £3,605 from day one. That fee is still typically far less than the interest you'd otherwise pay over the same period.

The transfer fee maths

The break-even question is simple: does the interest you avoid during the 0% window exceed the transfer fee? At 24.9% APR on £3,500, the monthly interest is around £73. A 3% fee costs £105 once. You break even after less than two months — everything after that is pure saving. Longer 0% periods on larger balances make the fee even more worthwhile, though the fee percentage itself may be slightly higher.

What happens at the end of the 0% period

This is where people get caught out. When the promotional period ends, any remaining balance reverts to the card's standard purchase or revert rate — often 20–30% APR. If you haven't cleared (or transferred again) by then, interest kicks in on whatever is left. The calculator above shows you exactly what that remaining balance and subsequent interest cost looks like.

Tips for making it work

Set up a direct debit immediately. Even if it's for the minimum payment, this protects the 0% offer. Missing a payment is the single most common way people lose their promotional rate.

Don't spend on the balance transfer card. Purchases on a BT card typically accrue interest at the standard rate from day one, and payments are often applied to the cheapest debt first — meaning your new spending can sit accruing interest while you pay off the transferred balance. Use a different card for daily spending.

Don't apply for multiple cards at once. Each application leaves a hard search on your credit file. Multiple applications in a short window can lower your credit score and reduce approval chances. Use an eligibility checker first — these use soft searches that don't affect your score.

Set a calendar reminder. Put a reminder two months before the 0% period ends. That gives you time to either clear the remaining balance, make a second balance transfer, or arrange a personal loan if neither is available.