Steve and Lisa's Mortgage Morsels

30 percent of the total credit score is based on a borrower's total outstanding debt. Revolving lines of credit, which allow a consumer to borrow as much or as little as desired up to a limit (versus installment loans where a set amount -- say, $20,000 plus interest for a car – is determined at the outset), are more heavily weighted. Credit cards are a type of revolving account. Since FICO views borrowers who habitually max out credit cards -- or who get very close to their credit limits -- as people who cannot handle debt responsibly, a borrower should maintain low credit card balances. Experts recommend that the amount owed should not exceed 30 percent of the individuals credit limit. That 30 percent rule of thumb applies to each individual credit card as well as the overall level of debt.

The final components of a FICO credit score get less weight in the score's calculation. "The remaining one-third of your score is determined by how long you have managed credit, to what degree you have pursued new credit recently and the variety of credit types you have successfully handled," Watts says.