Zero per cent is a rate, and the price can be somewhere else

Both approaches to interest-free credit work. What differs is what they cost you, and the cost is what this sets out.

Where the cost goes

A lender offering zero per cent still funds the money and still expects a return, so the cost appears somewhere else. On balance transfers it is usually an upfront fee charged as a percentage of the transferred amount. On retail finance it may be built into the price of the item, which is why cash discounts sometimes exist for non-finance buyers.

On credit cards it is the expectation that a proportion of customers will not clear the balance before the promotional rate ends.

Deferred interest is the one that catches people

Some interest-free arrangements do not waive interest but defer it, and apply the full accrued amount retrospectively if the balance is not cleared by the deadline. That means missing the deadline by a small margin can produce a charge covering the entire period at the standard rate.

On the balance sheet, whether an offer is genuinely interest-free or deferred is stated in the agreement and is the single most important thing to check. The two are described in very similar marketing language and behave completely differently.

The end date is the whole plan

An interest-free period only helps if the balance is gone before it expires, which requires dividing the balance by the number of months and paying that amount. Paying the minimum during a promotional period leaves a substantial balance to be repriced at the standard rate.

Setting a standing order for the calculated amount, rather than relying on minimums, is what converts the offer into a saving. A diary reminder one month before expiry gives time to clear or move the remainder.

Transfer fees need comparing against interest saved

A transfer fee is paid immediately and the interest saved accrues over the promotional period, so the comparison requires both numbers. For a large balance over a long promotional period, the fee is usually far smaller than the interest avoided. For a small balance that would be cleared in a few months anyway, the fee can exceed the saving.

Some offers have no fee and a shorter period, which suits balances that can be cleared quickly.

The conditions that void the offer

Missing a payment, exceeding the credit limit or paying late commonly terminates a promotional rate immediately. Transfers must usually be made within a defined window after opening, and transfers made later attract the standard rate. New spending on a card carrying a transferred balance can be charged at the standard purchase rate while payments are allocated elsewhere.

The arithmetic is straightforward: using one card for a transfer and never spending on it removes most of these failure modes.

This is general information, not advice about your particular position.

What the offer does not fix

Moving a balance reduces its cost; it does not reduce the amount owed, and the debt still has to be repaid. Repeated transfers can conceal a balance that never falls, which is a pattern worth checking against your own history.

Each application involves a credit search and a new account, which affects a credit file in the short term. Where borrowing is growing rather than shrinking, free debt advice is a better response than a further transfer.

Side by side

The takeaway

Divide the balance by the number of interest-free months and pay that. The offer is a deadline, not a discount.

Costs compound as reliably as returns do, and in the same direction.