Obviously, the higher your FICO credit score, the lower your payments. It is not a rocket science. The following charts are borrowed from myFICO and the rates are as of of June 4, 2009. You can get such charts anywhere. The date is not that important as the rates go up and down, but how the interest rates are affected by the credit score is.

30 Year Fixed Mortgage Chart

You can clearly see how credit score affects interest rate and monthly payment. On the $300,000
30 year fixed mortgage the interest rate difference between the highest range from 760 to 850 and the lowest from 620
to 639 results in 1.589%. Subsequently, monthly payment differs by $303, which amounts to $3,626 per year and cool $10,908 over just three years. I am not going to dwell on how much interest you will overpay over 30 years or even 10, since few homeowners stay that long in one place without moving out or refinancing. But if you have some credit issues and your score is what it is, then that is how it affects your interest rate for a year or two at least. And if your credit problems continue, so will your higher mortgage payments.

15 Year Home Equity Loan Chart

For those who forgot, home equity loan is the second installment loan on your home. Unlike the revolving home equity line of credit with variable rate which typically changes whenever Prime Rate is changed, equity loan interest rate is fixed for 5 or 10 years. The payments are for a $50,000 second loan which is amortized over 180 months. Again $133 difference between highest and lowest interest rate tiers clearly demonstrate how credit score affects interest rate.

36 Month Auto Loan Chart

The short term auto loan is affected the most. The rate difference in whopping 10.26%. The result is that someone with credit score of 563 pays $122 more each month than a person with 737 FICO score on a small $25,000 loan. And those auto loans are often hard to refinance, so it is $4,392 more in payments over 3 years. See also how credit score affects mortgage rate.