What date is used to calculate the patent term for a PCT application that entered the national stage in the U.S.?

The correct answer is the PCT filing date. In the context of a Patent Cooperation Treaty (PCT) application that enters the national stage in the United States, the U.S. Patent and Trademark Office (USPTO) uses the PCT filing date as the reference for calculating the patent term. This date is crucial because it sets the groundwork for determining the length of the patent protection afforded by subsequent national phase applications.

The patent term in the U.S. is typically 20 years from the earliest filing date of the patent application. For PCT applications, this earliest date is established as the international filing date, which corresponds to the date the initial PCT application was submitted. Thus, when the PCT application goes into the U.S. national phase, it retains its initial filing date globally recognized within the PCT framework, allowing for consistent timing across member countries.

Understanding this process is vital for applicants considering international protection for their inventions, as the PCT filing date directly influences not only the patent term but also factors like prior art determination and potential extensions.