But some new costs may fall on those who buy their own insurance in the individual market.
People who qualify for government subsidies would see a substantial drop in premiums, while those who don't qualify for subsidies could pay as much as 13 percent more in premiums than they do now, according to the nonpartisan Congressional Budget Office report. Individuals who buy their own coverage represent about 17 percent of the total insurance market.
Released just hours before the Senate took up debate on the $848 billion legislation, the CBO report offered ammunition to both sides in the debate over the health care overhaul legislation.
Supporters are hailing it as proof that the plan will help people who struggle to afford health care and change little for those covered by their employers.
"The analysis we received today indicates that whether you work for a small business, a large company or you work for yourself, the vast majority of Americans will see lower premiums than they would if we don't pass health reform," said Senate Finance Committee Chairman Max Baucus in a statement released by his office Monday.
But during the Senate floor debate Monday afternoon, Republican Sen. Charles Grassley said the new numbers only confirm fears that health reform efforts will raise costs.
"Millions of people who were expecting to pay lower costs will end up paying more in higher premiums," he said. "The Reid bill is not fixing the problem."
Findings from the report include:
-- Premiums paid by large companies or groups, representing 70 percent of the insurance market, would hold steady or drop by up to 3 percent.
-- Premiums paid by small employers would largely stay the same. But small employers who qualify for tax credits, representing about 12 percent of the market, would see rates drop by as much as 11 percent.
-- Individuals who buy insurance on the individual market would see rates rise by 10 percent to 13 percent. But more than half of these people -- 57 percent -- qualify for subsidies and would pay nearly 60 percent less.
The CBO said its estimate, which was requested by Sen. Evan Bayh, D-Ind., included a "substantial degree of uncertainty" due to various factors, including the number of people who purchase coverage.