"We are actually in a good or better position than we were at this time last year," Hemsley said. "But we think we are being cautious, and we think the market should be cautious as well."
UnitedHealth Group Inc. will deliver its first 2013 earnings forecast next month at its annual investor meeting.
In the third quarter, the health benefits provider earned $1.56 billion, or $1.50 per share, overall. That compares with $1.27 billion, or $1.17 per share, in last year's third quarter.
Analysts had forecast earnings of $1.34 per share, and UnitedHealth said earlier this month its net income would be at least $1.45 per share.
Revenue rose 8 percent to $27.3 billion. That fell short of average analyst expectations of $27.58 billion, according to FactSet.
UnitedHealth said Tuesday its third quarter was helped by Medicare and retirement revenue that swelled by $1.2 billion, as Medicare Advantage enrollment grew by 400,000 people compared with last year.
Medicare Advantage plans are privately run, subsidized versions of the government's Medicare program for the elderly and disabled people. UnitedHealth is the largest provider of these plans, and it made a couple of acquisitions within the past year to help spur growth. Big health insurers have been snapping up smaller Medicare Advantage plan providers to prepare for the millions of Baby Boomers who will become eligible for this coverage over the next couple decades.
Aside from the Medicare growth, the insurer also recorded a $390 million benefit in the quarter because claims left over from earlier periods came in lower than expected, which freed up money held in reserve. That compares with a $200 million benefit in last year's quarter.
UnitedHealth is the first major insurer to report earnings every quarter, and Goldman Sachs analyst Matthew Borsch said in a Tuesday morning research note the report should set a positive tone for the sector, which also includes WellPoint Inc. and Aetna Inc.