UPDATE 2-UnitedHealth's results top estimates, raises 2018 profit outlook

(Adds analyst estimates, sales in Optum business; updates shares)

Jan 16 (Reuters) - UnitedHealth Group Inc beat analysts' estimates with its fourth-quarter profit and revenue and raised its forecast for full-year earnings per share, citing gains from lower federal taxes.

Shares of the largest U.S. health insurer, which reiterated its full-year revenue outlook, rose 2.8 percent to $235 in premarket trading on Tuesday.

The company said it now expects 2018 full-year net earnings per share forecast range to be between $11.65 and $11.95, up from its prior forecast of $10.00 to $10.30 per share.

Corporate earnings in 2018 are expected to see a boost from the sweeping $1.5 trillion tax bill that President Donald Trump signed into law last month.

The health insurer said net earnings attributable to shareholders more than doubled to $3.62 billion, or $3.65 per share, in the quarter ended Dec. 31, from a year earlier.

The quarterly earnings included a one-time tax benefit of $1.21 per share. Excluding items, UnitedHealth earned $2.59 per share, beating analyst estimates of $2.51 per share.

Total revenue rose 9.5 percent to $52.06 billion, driven by growth across UnitedHealth's businesses.

Analyst on an average were expecting revenue of $51.5 billion, according to Thomson Reuters I/B/E/S.

Revenue from the company's Optum business, which manages drug benefits and offers healthcare data analytics services, rose 10 percent to $24.39 billion.

(Reporting by Divya Grover in Bengaluru; Editing by Arun Koyyur)