Doug Elmendorf, the CBO director, has previously attributed the slowdown to the recovering economy and "structural factors" in the healthcare system.
Supporters of President Obama's healthcare law say its reforms are behind the slower cost growth.
Tuesday's report also forecast a 5.5 percent decrease in Medicaid spending between 2013 and 2022 compared with estimates made last August.
Medicaid spending per person is expected to go down, the CBO explained, as a result of the Affordable Care Act's extension of eligibility to healthier adults.
The program will also see less enrollment than previously estimated, the CBO predicted.