"After the uncrewed flight tests, both companies will execute a flight test with crew prior to being certified by NASA for crew rotation missions", NASA communications specialist Stephanie Martin wrote in a blog post.
The first two on the list were initially slated for this summer, but a technical failure experienced during a recent test forced Boeing to revise the entire schedule until that problem is fixed.
If those uncrewed missions go well, Boeing and SpaceX will each follow with two crewed flights in 2019.
Part of Boeing's delay arose from a propellant leak in June during a launch-abort engine test in New Mexico.
SpaceX's Dragon crew ship, on display at the company's Hawthorne, Calif., factory in 2014.
NASA estimates have predicted even greater delays than what the agency formally announced August 2.More news: Apple becomes first-ever company valued at $1 trillion
The announcement is at 10 a.m. Friday at the Johnson Space Center.
The announcement is a big deal because the last American crew-carrying spacecraft - NASA's fleet of four space shuttle orbiters - retired in July 2011.
The first test flights for new spacecraft designed by commercial companies in collaboration with NASA to carry astronauts to and from the International Space Station from the United States are known as Demo-1 for SpaceX and Orbital Flight Test for Boeing. They're both the result of NASA's Commercial Crew Program: a almost 10-year-long, $8-billion effort to maintain access to orbit for USA astronauts.
If this second test is successful, Boeing will launch Spacecraft 2 along with its first passengers toward the middle of 2019.
However, both companies still have to prove that their vehicles can fly to the ISS and return safely to Earth.
Four of the eight astronauts will nearly certainly be Bob Behnken, Eric Boe, Doug Hurley, and Sunita "Suni" Williams. The uncrewed test flight will not take place before the end of 2018 or early 2019 and the crewed test flight in mid-2019. Surprisingly, only 3.0 percent of adults in the survey said NASA's top focus should be sending astronauts to the moon, while a mere 8.0 percent said a human trip to Mars or other planets should be a top priority. NASA Administrator Jim Bridenstine will preside over the event, which will begin at 11 a.m. EDT on NASA Television and the agency's website. On Sept. 16, 2014, the agency announced that Boeing and SpaceX would share $6.8 billion to develop independent space taxis, the first new US crewed spacecraft since the shuttle.