Why did my credit card APR go up even though I never missed a payment?

Most credit cards carry a variable APR tied to the prime rate. When the Federal Reserve raises rates, the prime rate rises, and your card's APR rises with it, usually within a billing cycle or two, no missed payment required. Your cardholder agreement spells out the formula, typically prime plus a margin.

Issuers can also raise your rate for other reasons after the first year: a general repricing with 45 days' written notice under the CARD Act, or a change in your risk profile. What they generally cannot do is raise the rate on your existing balance in year one, except for a promotional rate ending or a payment more than 60 days late. If the increase surprises you, call and ask why, and whether they'll reduce it.