Basics

• The national, federal, U.S. and Wall Street Journal prime interest rate indexes are the ones most referenced by investors and analysts. The prime interest rate is defined as "the base rate on corporate loans posted by at least 75% of the nation's 30 largest banks," according to the Wall Street Journal.
  
  

Variable Rate Loans

• Variable rate credit cards are adjusted according to changes in the prime interest rate. When prime rates are trending upward, the cost of short-term credit increases. If the prime rate falls, your borrowing costs decrease in the short-term.
  
  

Trends

• The prime interest rate has been as high as 9.5 percent in the 21st century (May 2000) and is at a current low point of 3.25 percent, where it has remained for much of 2010. The prime rate trends based on Central Bank policy of increasing, decreasing or stable rates.