NASA and SpaceX are now aiming for a March debut of the first commercial crew capsule. The first Starliner flight with astronauts would be August at best.
"These adjustments allow for completion of necessary hardware testing, data verification, remaining NASA and provider reviews, as well as training of flight controllers and mission managers", they added.
No one will be on board for the crew Dragon's inaugural test flight to the International Space Station.
NASA's final now contracted Soyuz flight is scheduled for launch in July.
The commercial crew program has suffered multiple delays due to technical issues and congressional funding shortfalls, but NASA managers say the new spacecraft are close to being ready for their initial test flights.
SpaceX, though, has been making progress, including rolling out the Crew Dragon spacecraft atop its Falcon 9 rocket to Launch Complex 39A at the Kennedy Space Center in early January for tests.
"The agency now is targeting March 2 for launch of SpaceX's Crew Dragon on its uncrewed Demo-1 test flight". "NASA has been working together with SpaceX and Boeing to make sure we are ready to conduct these test flights and get ready to learn critical information that will further help us to fly our crews safely". The Crew Dragon is equipped with rocket engines that can quickly push the ship away from a malfunctioning booster at any point from launch pad to orbit.
If all goes well, the first manned flight is scheduled for July 2019. The test flight had been planned for mid June, but sources say it's now targeted for July.
Boeing is shooting for an April launch of its first Starliner capsule without a crew.
Then will come huge milestones - crewed test flights to the ISS. Unlike the Crew Dragon, the Starliner is created to land in the western United States using parachutes and airbags.
It would be the first launch of USA astronauts into orbit, from US soil, since NASA's shuttle program ended in 2011.
If all goes well, operational crew rotation flights could begin well before the end of the year.