UnitedHealth Group's third-quarter earnings soared 26 percent to beat Wall Street expectations as the nation's largest health insurer sold more coverage to retirees and continued to grow its business outside insurance.

The insurer said Tuesday it gained nearly 2 million more customers compared to last year's quarter, largely due to growth in its Medicare and retirement business. UnitedHealth is the nation's largest provider of Medicare Advantage plans, which are privately run versions of the government's Medicare program for the elderly and disabled people.

That gain more than countered a revenue hit the insurer took from the deferral of an insurance tax and the company's decision to scale back its presence on the Affordable Care Act's insurance marketplaces.

Operating earnings grew 14 percent to $2.4 billion for the company's main business, health insurance. But its Optum segment also saw earnings increase to $1.7 billion.

Optum provides pharmacy benefits management and technology services and also operates clinics and doctor's offices.

Overall, the Minnetonka, Minnesota, company earned nearly $2.49 billion as revenue grew 9 percent to $50.32 billion. Adjusted earnings totaled $2.66 per share.

Analysts expected earnings of $2.56 per share on $50.35 billion in revenue, according to FactSet.

UnitedHealth Group Inc. also said Tuesday that it expects 2017 earnings to approach $10 per share. That's up from a forecast it made in July for between $9.75 and $9.90 per share

Analysts expect $9.86 per share.