There is no extra year in this case. The relevant law is -
35 U.S.C. 154 Contents and term of patent; provisional rights.
(a) IN GENERAL.—
(2) TERM.—Subject to the payment of fees under this title, such grant shall be for a term beginning on the date on which the patent issues and ending 20 years from the date on which the application for the patent was filed in the United States or, if the application contains a specific reference to an earlier filed application or applications under section 120, 121, 365(c), or 386(c) from the date on which the earliest such application was filed.
There is an exception if the earliest application is a provisional. Then it could expire 21 years from the provisional fining date, assuming the non-provisional or pct was filed on the last day of the term of the provisional.