How can I improve my score? Read our lips: Pay your bills on time. More than one-third of your score is based on your payment history, and the later you are, the more points you lose. If you've fallen behind, pay up now. Negative items generally affect your score for up to seven years, but as time goes by their impact lessens.

How much you owe makes up another third of your score. Your "credit utilization" ratio -- the percentage of your credit limit that you've actually used -- is more important than the amount of credit to which you have access. Watts recommends keeping the balance on your cards below 25% of your available credit, or $2,500 on a card with a $10,000 ceiling. What counts is the total amount you've charged, even if you plan to pay the bill in full.

The length of your credit history accounts for 15% of your FICO score. Getting a lot of new credit within a short time span can hurt your score because it lowers the average age of your accounts.

About 10% of your score is based on new credit. If you open a flurry of new accounts, lenders worry that you might go on a borrowing binge. "Don't apply for new credit within three to six months before applying for a mortgage," recommends Maxine Sweet, vice-president of consumer education for the credit bureau Experian.

Your credit report records an inquiry every time a potential lender requests a copy of the report, and that can make lenders nervous. Because more people shop online for car loans and mortgages, Fair Isaac eased its rules: If your report shows inquiries from several car or mortgage lenders within 14 days, it's assumed you're shopping for a single loan. The newest version of the FICO score expands that to 45 days.

Finally, 10% of your score depends on the types of credit you use. Your experience with revolving credit, such as credit cards, on which you control how much you charge and pay off each month, carries more weight than installment debt, such as car loans and mortgages, with fixed payments.

Can closing old accounts help my score? That's the most common misconception about credit scores. Closing old accounts can actually hurt your score because it raises your utilization ratio. Owing $5,000 looks a lot better when you have a $20,000 maximum on all of your credit cards -- a utilization ratio of 25% -- than it does when you have a limit of $7,000 -- a ratio of more than 70%.

Even though your credit score will dip temporarily, it's okay to close accounts as long as you don't plan to apply for a loan within the next few months. That will give your score time to recover. Close department- store accounts and new cards first.

Can overdue library books really affect my score? They sure can. To beef up their revenues, local governments are hiring collection agencies to track down the money people owe in library fines, unpaid parking tickets and other fees. If an account goes into collection, it can destroy your credit score. "That's considered a serious delinquency that could drop a high FICO score by 100 points," says Watts.

A new version of the FICO score ignores delinquencies on accounts for which the past-due amount is less than $100. But most lenders still use the older version of the score.

If you're disputing a small charge, it might be better to pay the bill rather than continue to fight or take the issue to small-claims court. "Some consumers refuse to pay on principle, but companies that can report you to a collection agency have the power to ruin your credit," says Gerri Detweiler, credit expert for EverydayWealth.com and author of The Ultimate Credit Handbook. Ask to have the collection accounts removed from your record in exchange for payment.

Will my score go down if I marry someone with a bad score? Not necessarily. There are no joint credit reports or scores, so getting married in itself won't lower your score. But becoming a co-signer on an account with a bad history will tarnish your record. And lenders will look at both credit histories if you apply for a loan together -- and the bad one could carry more weight. See if you can qualify with only one income, or wait to apply until your spouse's score improves.

What should I do if I have a lot of black marks on my credit history? Continue using your cards, but clean up your act. Pay your bills, keep your account balances low, and be sparing in opening new accounts. As long you use credit conservatively, your score can rebound surprisingly quickly, says Watts. "We've seen cases of bankruptcy in which borrowers have qualified for a premium mortgage in three years."

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