While the USN currently has 11 nuclear powered super carriers (10 Nimitz class and 1 Ford class) at any one time there is usually at least 1 undergoing Refuelling and Complex Overhaul (RCOH), a process that takes them out of service for at least 4 years at a time.
The George Washington CVN-73 started her RCOH in Aug 2017, and has only returned to sea again last month to run post refit trials. She is expected to become fully operational again in 2024.
The John C Stennis CVN-74 began her RCOH in May 2021 and will not be back in service until at least 2025, and probably later, given delays in earlier ships.
Given the regular round of refits and work ups and the number of available air wings (see below) there are never 11 or even 10 available at one time. One ship, currently the CVN-76 Ronald Reagan, has its Home Port at Yokosuka, Japan. 4 are based on the US west coast and 4 on the east coast.
Getting CVN-78 Gerald R Ford operational has proved a lengthy task. First of a new class, Ford commissioned in July 2017, and was packed with new technology - new EMALS catapults, new arrester gear, new weapon elevators as well as new radars, which have provided many headaches. She has only begun her first fully operational deployment in 2023.
As for the new Ford class the completion dates are currently expected to be:-
CVN-79 John F Kennedy - as of March 2023 her delivery date has been pushed back from 2024 to 2025.
The next Ford-class aircraft carrier will now deliver to the Navy in 2025, one year later than the service’s most recent projection, according to Fiscal Year 2024 budget documents released this week. The Navy delayed future carrier John F. Kennedy’s (CVN-79) delivery date from June 2024 so the...
news.usni.org
CVN-80 Enterprise - expected completion 2028
CVN-81 Doris Miller - expected completion 2032.
Meanwhile CVN-68 Nimitz is scheduled to be taken out of service in FY25 I.e. between 1 Oct 2024 and 30 Sept 2025, just as the Kennedy enters service.
More importantly, there are currently only 9 Carrier Air Wings (5 in the Pacific and 4 in the Atlantic) plus what is known as a Tactical Support Wing (previously a Reserve Carrier Air Wing) which is responsible for operational and training support of the main CVW. Only 2 of its 5 squadrons fly carrier capable aircraft unlike in the old days when the Reserve Wings could be carrier deployed in an emergency. CVW-5 is based at MCAS Iwakuni in Japan for the Ronald Reagan.
So the number of US carriers will never rise above 9 in service at one time.
You can follow their movements here.
Edit:- Nimitz first commissioned in May 1975 and had her RCOH between 1998 and 2001. So she will be 50 by the time she leaves service, with John F Kennedy as her replacement.
Eisenhower first commissioned in Oct 1977 and had her RCOH between 1995 and 1998. Her replacement will be the Enterprise around 2028/29, when she will be 50+ years old.
Vinson first commissioned in March 1982 and had her RCOH between 2005 and 2009. She will be 50 in 2032 just as the Doris Miller is scheduled to join the fleet.
The next oldest is the Theodore Roosevelt first commissioned in Oct 1986 and given her RCOH between 2009 and 2013.