U.S. long-term mortgage rates rose this week for the fourth straight week, though they remain historically low as a spur to home sales in the spring buying season.

Mortgage buyer Freddie Mac said Thursday the average rate on the 30-year, fixed-rate mortgage increased to 4.20% from 4.17% last week. By contrast, a year ago the benchmark rate stood at 4.58%.

The average rate for 15-year, fixed-rate home loans rose this week to 3.64% from 3.62% last week.

After peaking at nearly 5% in November, long-term rates started trending downward, helping to boost home sales after a rocky 2018.

Despite the recent increases, lower borrowing rates and improved affordability of homes "should push housing activity higher in the coming months," said Freddie Mac chief economist Sam Khater.

Freddie Mac surveys lenders across the country between Monday and Wednesday each week to compile its mortgage rate figures.

The average doesn't include extra fees, known as points, which most borrowers must pay to get the lowest rates.

The average fee on 30-year fixed-rate mortgages was unchanged this week at 0.5 point.

The average fee for the 15-year mortgage also remained at 0.5 point.

The average rate for five-year adjustable-rate mortgages slipped to 3.77% from 3.78% last week. The fee rose to 0.4 point from 0.3 point.