Chapter 4 - Physical Presence
An applicant for naturalization is generally required to have been physically present in the United States for at least half the time for which his or her continuous residence is required. Applicants for naturalization under INA 316(a) are required to demonstrate physical presence in the United States for at least 30 months (at least 913 days) before filing the application. 
Physical presence refers to the number of days the applicant must physically be present in the United States during the statutory period up to the date of filing for naturalization. The continuous residence  and physical presence requirements are interrelated but each must be satisfied for naturalization.
USCIS will count the day that an applicant departs from the United States and the day he or she returns as days of physical presence within the United States for naturalization purposes. 
Mere possession of a Permanent Resident Card (PRC) for the period of time required for physical presence does not in itself establish the applicant’s physical presence for naturalization purposes. The applicant must demonstrate actual physical presence in the United States through documentation. USCIS will review all of the relevant records to assist with the determination of whether the applicant has met the required period of physical presence. The applicant's testimony will also be considered in determining whether the applicant met the required period of physical presence.
[^ 3] USCIS will only count residence in the Commonwealth of the Northern Mariana Islands on or after November 28, 2009, as time counted for physical presence within the United States for naturalization purposes.