From the March, 27 2013 Congressional Research Service report:
The Navy’s proposed FY2013 budget requests $564.9 million for continued research and development work on the Ohio replacement program (ORP), a program to design and build a new class of 12 ballistic missile submarines (SSBNs) to replace the Navy’s current force of 14 Ohio- class SSBNs. The Ohio replacement program is also known as the SSBN(X) program.
Under the Navy’s FY2012 budget, the first Ohio replacement boat was scheduled to be procured in FY2019, and Ohio replacement boats were to enter service on a schedule that would maintain the Navy’s SSBN force at 12 boats. The Navy’s proposed FY2013 budget defers the procurement of the first Ohio replacement boat by two years, to FY2021. As a result of this deferment, the Navy’s SSBN force will drop to 11 or 10 boats for the period FY2029-FY2041.