The U.S. budget deficit for fiscal year 2014 will be an estimated $506 billion, a slight increase from the $492 billion projected in April, based on lower-than-expected corporate tax receipts, the Congressional Budget Office said on Wednesday.

U.S. budget deficits are expected to remain less than 3 percent of GDP through 2018 but grow after that, rising to nearly 4 percent of GDP in 2022, CBO said. That is because revenues will grow only slightly faster than the economy and spending is projected to increase more rapidly, the budget agency said.

CBO said a substantial amount of slack remains in the U.S. labor market due to the lower participation rate and an elevated number of people working part time.

(Reporting by Mark Felsenthal; Editing by Eric Beech)