Mortgage rates were down slightly this week, with the average 30-year fixed mortgage rate dipping to 5.18 percent. According to Bankrate.com's weekly national survey, the average 30-year fixed mortgage has an average of 0.44 discount and origination points.

The average 15-year fixed rate mortgage retreated to 4.72 percent, and the average jumbo 30-year fixed rate slumped to 6.69 percent. Adjustable rate mortgages were mixed, with the average 1-year ARM rising to 5.28 percent while the 5/1 ARM sank to 5.12 percent.

Recent weeks have produced relatively little fluctuation in mortgage rates, in contrast to the sharp ups and downs seen earlier in the year. Even the weak economic data of the past several days didn't push mortgage rates significantly lower, mostly because lenders are already up to their necks in applications. The ailing economy and inundated lenders are the two factors that will likely keep mortgage rates rangebound in the weeks to come.

Mortgage rates remain at historic lows. Six months ago, the average 30-year fixed mortgage rate was 6.74 percent, meaning a $200,000 loan would have carried a monthly payment of $1,295.87. With the average rate now more than 1.5 percentage points lower at 5.18 percent, the monthly payment for the same size loan would be $1,095.75, a savings of $200 per month for a homeowner refinancing now.

SURVEY RESULTS

30-year fixed: 5.18% - down from 5.2% last week (avg. points: 0.44)

15-year fixed: 4.72% - down from 4.75% last week (avg. points: 0.38)

5/1 ARM: 5.12% - down from 5.27% last week (avg. points: 0.49)

Bankrate's national weekly mortgage survey is conducted each Wednesday from data provided by the top 10 banks and thrifts in the top 10 markets.