WASHINGTON (AP) ― Solid economic growth will help the U.S. budget deficit shrink this year to its lowest level since President Barack Obama took office, according to congressional estimates released Monday.

The Congressional Budget Office says the deficit will be $468 billion for the budget year that ends in September. That’s slightly less than last year’s $483 billion deficit.

As a share of the economy, CBO says this year’s deficit will be slightly below the historical average of the past 50 years.

The budget agency also says the number of U.S. residents without health insurance will drop substantially ― from 42 million last year to 36 million this year ― largely because of Obama’s health law. These numbers don’t include people who are in the U.S. illegally, who are ineligible for subsidies under the health law.

In a report released Monday, CBO projects solid economic growth for the next few years. The official scorekeeper of Congress also expects unemployment to drop slightly.

“In CBO’s estimation, increases in consumer spending, business investment and residential investment will drive the economic expansion this year and over the next few years,” the report said.

CBO also cited wage increases, rising wealth and the recent decline in oil prices.

For future years however, CBO issued a warning: Beyond 2018, deficits will start rising again as more baby boomers retire and enroll in Social Security and Medicare. By 2025, annual budget deficits could once again top $1 trillion, unless Congress acts.

At that point, government pension benefits would account for one-quarter of all federal spending, said CBO Director Douglas Elmendorf.

“The underlying point is that we have a handful of very large federal programs that provide benefits to older Americans,” Elmendorf said. “And with the rising number of older Americans and a rising cost of health care, those programs get much more expensive.”

Obama inherited an economy in recession when he took office. The annual deficit topped $1 trillion for each of his first four years in office, including a record $1.4 trillion in 2009.

The federal budget deficit became a big issue during Obama’s early years in office. In 2011, Obama and congressional Republicans struck a deal that resulted in significant spending cuts at many government agencies. At the start of 2013, Obama persuaded Congress to further address the deficit by raising taxes on top earners.

Declining budget deficits, however, could reduce pressure on Congress to continue addressing the government’s finances.

“Over the last few years as deficits have fallen, so too has the effectiveness of Republican rhetoric about a `big government’ boogeyman,” said Sen. Charles E. Schumer, a Demnocrat. “Now is the time for Republicans to join with Democrats to invest in constructive programs that help middle-class Americans climb the ladder and achieve the American dream.”

Republicans, however, signaled that they are not finished cutting spending.

“Thanks to Republicans’ efforts to cut spending this year’s deficit is projected to be smaller, but in order to balance the budget we must address the true drivers of our debt,” said Cory Fritz, a spokesman for House Speaker John Boehner, a Republican. “Real, robust economic growth won’t occur until we solve our government’s spending problem.”

CBO projects that the economy will grow at an annual rate of 3 percent in both 2015 and 2016. In later years, however, CBO projects slower economic growth as more baby boomers retire and the labor force grows more slowly than it did in the 1980s and 1990s.

CBO projects the unemployment rate will gradually decrease to 5.3 percent in 2017. It is now 5.6 percent.