WASHINGTON — The average rate on a 30-year mortgage in the U.S. rose for the third straight week to its highest level since mid-July, reflecting a recent jump in the bond yields that lenders use as a guide to price home loans.

The rate rose to 6.85 percent from 6.72 percent last week, mortgage buyer Freddie Mac said Thursday. One year ago, the rate on a 30-year mortgage averaged 6.61 percent.

The average rate on a 30-year mortgage is now the highest it has been since the week of July 11, when it was at 6.89 percent. It dipped as low as 6.08 percent in September — a two-year low — and as high as 7.22 percent in May.

Most economists forecast the average rate on a 30-year mortgage to remain above 6 percent next year, with some including an upper range as high as 6.8 percent. That range would be largely in line with where rates have hovered this year.

Borrowing costs on 15-year fixed-rate mortgages also rose. The average rate increased to 6 percent from 5.92 percent last week. A year ago, it averaged 5.93 percent.

Elevated mortgage rates and rising home prices have kept homeownership out of reach of many would-be homebuyers. While sales of previously occupied U.S. homes rose in November for the second straight month, the housing market remains in a slump and is on track for its worst year since 1995.