To boost your credit, try this tool

I applied for a car loan and was told that my credit score is too low to qualify me for the best rate, so I'd like to try to improve it. How can I find out whether closing old accounts or making other changes would help?

TransUnion has a free credit score simulator on its affiliated website, http://www.truecredit.com (click on Learn, then on Credit Score Simulator), that lets you play around with the variables to see how certain changes would affect your score. Fair Isaac, the company that invented the FICO score, also offers a simulator as part of FICO Deluxe ($47.85 for a one-time purchase or $42.84 annually), which includes credit scores and reports from all three major national credit bureaus. Keep in mind that the law entitles you to a free copy of each of those three reports (excluding credit scores) annually from http://www.annualcreditreport.com.