Congress is holding hearings today to denounce the credit card practice of raising interest rates of customers who pay on time just because their credit score went down. The real investigation should be of the credit reporting agencies and how they determine those mysterious credit scores. Also, a credit score should be available for free at least once a year just like a credit report is free yearly.

This issue should have been part of the new bankruptcy bill that Congress passed in 2005 when it was clear that the credit card company practices of jacking up interest rates on credit cards to between 25% and 30% was helping to push people over the edge to bankruptcy. But Congress ignored the problem and just made it harder to file for bankruptcy.

Why can credit card companies charge so usurious rates? That's because credit card rates are set on a state by state basis and some states allow more freedom to jack up rates. That's why credit cards are based in states like North Dakota or Delaware that allow these outrageous rates.

Many credit card agreements tell you in small print that if your credit score goes down, or if you miss a payment on another credit card, your rate will be hiked, but few people realize this provision exists. So what can cause your credit score to go down? Here are some biggies I found when I was researching my book, the Complete Idiot's Guide to Improving Your Credit Score:

• Paying one card late can reduce your credit score by 55 to 105 points. The better your credit score, the more your score is decreased.
• If you max out all your cards, your credit score will decrease by 50 to 100 points.
• If you miss payments on all your credit cards, your score would go down by 65 to 125.
• Bankruptcy is of course the biggest hit. If you declare bankruptcy, your score will go down by 205 to 265 points.

The key to a good credit score is to pay your cards on time and not to max out your cards. You get the best score when you pay your cards on time and use only about 20% of your allowable credit limit on your cards.

Lita Epstein has written more than 20 books including the Complete Idiot's Guide to Improving Your Credit Score due out this month.