Credit cards only get expensive when you carry a balance. If you pay your full statement balance by the due date, the grace period means your purchases usually owe no interest at all.

Carry a balance, though, and interest accrues — often daily — at your card's APR. Because it compounds, a balance that lingers can cost far more than the original purchase. Cash advances are worse still: they typically skip the grace period and charge a higher rate from day one.

The single most valuable habit is paying in full each month. If you can't, pay as much above the minimum as you can — our payoff calculator shows how much faster that clears the balance.