Feb 3 (Reuters) - Reinsurer Everest Group EG.N swung to a fourth-quarter loss on Monday, hit by a one-time charge tied to loss reserves in its U.S. casualty lines business.

The company last week disclosed that its fourth-quarter and full-year 2024 earnings will include a one-time charge of $1.5 billion tied to prior year's loss reserves and a further $229 million of current accident year strengthening.

A loss reserve refers to an insurer's projected liability for future claim payouts.

Everest also expects its pre-tax net catastrophe loss from California wildfires to be in the range of $350 million to $450 million for the first quarter of 2025.

Bermuda-based Everest offers property, casualty and specialty reinsurance and insurance services, and operates in more than 100 countries across six continents.

Insurance spending has remained robust despite economic uncertainties, as businesses and individuals prioritize coverage to guard against risks, including natural disasters, cyber attacks and health emergencies.

The company said its gross written premiums in its reinsurance business rose 12.6% to about $3.3 billion in the reported quarter.

Everest's investments raked in higher returns amid a bullish equity market and an overall higher interest rate environment that helped bond yields.

The company's net investment income rose to $473 million from $411 million in the prior year's fourth quarter, driven by a larger asset base as well as strong core fixed income investment returns.

Everest reported a net operating income of $630 million, or $14.62 per share, in the third quarter of 2024.

The company's net operating loss came in at $780 million, or $18.39 per diluted share in the fourth quarter ended Dec. 31, versus net operating income of $1.1 billion, equal to $25.18 per diluted share, a year ago.

(Reporting by Jaiveer Singh Shekhawat in Bengaluru; Editing by Mohammed Safi Shamsi)

((JaiveerSingh.Shekhawat@thomsonreuters.com;))