The U.S. economy will grow at 3.1 percent in 2018, according to updated projections by the Congressional Budget Office (CBO), down from its April estimate of 3.3 percent.

The updated estimate projects that the 4.1 percent second quarter spike of real GDP will come back down in the third and fourth quarters.

"Such moderation occurs because several factors that boosted second-quarter growth — including a rebound in the growth of consumer spending from a weak first quarter and a surge in agricultural exports — are expected to either fade or reverse," the CBO report said.

As in April, the updated estimate sees the economy growing at 2.4 percent in 2019, below its 2017 levels of 2.6 percent.

"In 2019, the pace of GDP growth slows to 2.4 percent in the agency’s forecast as growth in business investment and government purchases slows," the report said.

The CBO also ticked down its estimate of how fast the economy will grow in the latter half of the upcoming decade. While the April estimate projected growth of 1.7 percent from from 2020-2026 and 1.8 percent on average in 2027 and 2028, the new update estimates that growth would drop to 1.6 percent in 2021 and 2022 and remain at 1.7 percent from 2023-2028.

The main reasons for the adjustment were an updated accounting of how much spending the government would do, leading to less fiscal stimulus, and updated projections of lower interest rate increases.

The projections run counter to claims from the Trump administration, which has repeatedly said that its policies could deliver consistent growth of 3 percent over a decade, if not higher. If CBO's projections are correct, 2018 will be the only year it will meet that goal.

Even so, 2018 is set to be the first year since 2005 to surpass 3 percent overall growth.