With the spring buying season underway, mortgage buyer Freddie Mac said Thursday the average rate on 30-year, fixed-rate mortgages slipped to 4.55 percent from 4.58 percent last week. By contrast, the benchmark rate averaged 4.02 percent a year ago.

The average rate on 15-year, fixed-rate loans ticked up to 4.03 percent from 4.02 percent last week.

Despite higher borrowing costs and home prices, demand for home purchases has grown in the spring buying season as the economic outlook has continued to improve and bolstered consumer confidence.

First-time homebuyers accounted for 46 percent of mortgage loans taken out from January through April, up from 43 percent in the first four months of last year, according to Freddie Mac’s data.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country between Monday and Wednesday each week.

The average doesn’t include extra fees, known as points, which most borrowers must pay to get the lowest rates. The fees on 30-year and 15-year fixed-rate mortgages were unchanged from last week at 0.5 point and 0.4 point, respectively.

The average rate for five-year adjustable-rate mortgages fell to 3.69 percent from 3.74 percent last week. The fee remained at 0.3 percent