It found quoted rates of APR can vary according to whether interest is charged on interest, and whether there is an interest-free period.

BBC: Which? has made a "supercomplaint" to the OFT

Store cards don't pose a problem if you are disciplined enough to pay off the balance within the interest-free period (typically between 35 and 55 days).

BBC: NEWS | Business | Understanding store card debt

For instance, Apple offers customers up to 18 months interest-free on purchases on a card from Barclaycard US. But if you don't pay off that specific purchase in the interest-free period, you'll face a variable annual percentage rate that's currently about 23%, according to the Apple website.

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