Interest rates
How a credit card's APR actually works
How your APR becomes a daily rate, when the grace period means no interest, and how purchase, cash advance and penalty APRs differ.
Guides
Card costs
What a credit card really costs in a year
How to add up annual, monthly and usage fees plus interest, with a worked example and a guide to reading the rate and fee table.
Card basics
How credit limits are set, and what happens if you go over
What your credit limit covers, what issuers look at when they set it, how it can change, and the rules on going over it.