Average long-term U.S. mortgage rates surged this week, marking their largest one-week gain this year.

Mortgage company Freddie Mac said Thursday the nationwide average for a 30-year loan jumped to 4.23 percent from 4.12 percent last week. The average for a 15-year mortgage, a popular choice for people who are refinancing, rose to 3.37 percent from 3.26 percent.

At 4.23 percent, the rate on a 30-year mortgage is at its highest level since the week ended May 1, though it is still at a historically low level.

Mortgage rates often follow the yield on the 10-year Treasury note. The 10-year note traded at 2.62 percent Wednesday, up sharply from 2.54 percent a week earlier. It was trading at 2.63 percent Thursday morning. Bond yields rise when bond prices fall.

The increase in the yield on the benchmark Treasury bond was stoked by speculation in financial markets that the Federal Reserve might abandon its nearly 6-year-old policy of keeping short-term rates at record lows. But at their meeting this week that ended Wednesday, Fed policymakers decided to keep the low rates, at least for a few more months.

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. One point equals 1 percent of the loan amount.

The average fee for a 30-year mortgage was unchanged from last week at 0.5 point. The fee for a 15-year mortgage also remained at 0.5 point.

The average rate on a five-year adjustable-rate mortgage rose to 3.06 percent from 2.99 percent. The fee was stable at 0.5 point.

For a one-year ARM, the average rate fell to 2.43 percent from 2.45 percent. The fee held at 0.4 point.

(AP)