Radian Group Inc., the second-largest U.S. mortgage insurer, posted its fourth straight quarterly loss on a charge tied to derivatives.

The second-quarter net loss of $475.1 million, or $4.31 a share, compares with a profit of $231.9 million, or $2.82, the year earlier, the Philadelphia company said Tuesday.

Excluding the charge for derivatives, the loss was $1.22 a share, which is wider than the 78-cent loss that was the average of seven analysts' estimates.

Radian's credit spreads narrowed in the second quarter as the insurer raised capital in a share sale.

Accounting rules say insurers increase the cost of liabilities when their credit improves, contributing to derivative charges.

"Results include significant fair-value impact from the tightening of Radian's credit spread and continued uncertainty regarding the aged delinquencies in our mortgage insurance book," Radian's chief executive officer, S.A. Ibrahim, said in a press release.

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