As per: https://www.uscis.gov/green-card/after-we-grant-your-green-card/international-travel-as-a-permanent-resident
Generally, you can stay outside the U.S. for up to one year. If you have been issued a Re-Entry Permit, which applicants must apply for while in the U.S., you can stay outside the United States as long as your Re-Entry Permit has not expired. Please note, per USCIS, the abandonment of residency may be found to have occurred on trips of less than a year outside of the United States if is determined you did not intend to make the U.S. your permanent residence.
Additionally, absences from the United States of six months or more may disrupt the continuous residency required for naturalization. If your absence is one year or longer and you wish to preserve your continuous residency in the United States for naturalization purposes, you may file an Application to Preserve Residence for Naturalization Purposes on Form N-470. For more information, please see the Continuous Residence and Physical Presence Requirements page.
International Travel
U.S. immigration law assumes that a person admitted to the United States as an immigrant will live in the United States permanently. Remaining outside the United States for more than one year may result in a loss of Lawful Permanent Resident status.
U.S. government personnel (military and direct-hire civil service employees) and their spouses and minor children who hold Lawful Resident status of the United States may remain outside of the United States for the duration of an official overseas assignment plus four months without losing their resident status. Exceptions exist for family members of military service members.
All other immigrants who hold Lawful Permanent Resident status and reside outside of the United States for more than one year without prior approval from U.S. Citizenship and Immigration Services (USCIS) must obtain a new immigrant visa to return to the United States. Prior approval from USCIS consists of a re-entry permit which can only be applied for in the United States. The holder of a USCIS re-entry permit may remain outside of the United States during the validity period of the re-entry permit, normally up to two years. For more details on applying for a re-entry permit please visit the USCIS website.
A former immigrant who has lost permanent resident status and desires to return to the United States as an immigrant must obtain a new immigrant visa based on either an approved immigrant petition or Returning Resident status. A U.S. relative (spouse, parent, offspring, or sibling) or U.S. employer may file an immigrant petition on behalf of the former immigrant in the normal manner. Information on the various types of immigrant and employment based petitions are contained elsewhere in this website.
An application for Returning Resident status requires evidence of the applicant’s continuing, unbroken ties to the United States; that the stay outside the United States was truly beyond the applicant’s control; and that the intent of the applicant was to always return to the United States. Evidence may consist of continuous compliance with U.S. tax law, ownership of property and assets in the United States, and maintenance of U.S. licenses and memberships. Having U.S. relatives, attending school overseas, or stating an intent to return is generally insufficient.To apply for Returning Resident status,see Returning Resident Visas Checklist.
A Lawful Permanent Resident (LPR) of the United States who has stayed abroad for less than one year or within the validity of I-327 (re-entry permit)and wishes to re-enter the United States has to present a Green Card (Form I-551, Permanent Resident Card) in order to be permitted to board a flight to the United States. If your Green Card has been lost, stolen, or damaged, you can apply for a Boarding Foil, which permits the airline to transport you back to the United States. For more details please visit our page on Boarding Foils.
Expired/Expiring Green Card
If you are outside the United States and your Green Card will expire within six months (but you will return within one year of your departure from the United States and before the card expires), you should file for your renewal card as soon as you return to the United States.
If you have one of the following items, a boarding foil is not required:
- An expired Permanent Resident Card with a 10-year expiration date
- An expired Permanent Resident Card with two-year validity, AND a Form I-797, Notice of Action, indicating that status is extended.
If you have an expired Green Card with a 2-year expiration date AND a Form I-797, Notice of Action, showing that you have filed a Form I-751 or Form I-829 to remove the conditions on your Permanent Resident status, the Form I-797 extends the validity of the card for length of time specified on the form. - Orders from the U.S. government (civilian or military) showing that time outside the Unites States was on official government business.
- A valid re-entry permit
If you meet the criteria above, consult your air carrier prior to completion of an I-131A and payment of the fee.
Re-Entry Permit
If you plan to stay outside of the United States for more than one year but less than two years, you will need a re-entry permit for readmission. You must be physically present in the United States when you file the Form I-131 to apply for the permit. A re-entry permit may be sent to a U.S. Embassy or Consulate abroad for you to pick up, if you request it when you file your application. Departure from the Unites States before a decision is made on a re-entry permit application does not affect the application.
Generally, a re-entry permit is issued for two years from the date of issuance. However, a re-entry permit issued to a Conditional Resident is generally valid either two years from the date of issuance or until the date by which the Conditional Resident must apply for removal of the conditions on his or her status, whichever date comes first.
https://www.uscis.gov/policy-manual/volume-12-part-d-chapter-3
https://www.ecfr.gov/current/title-8/chapter-I/subchapter-C/part-316/section-316.5
General requirements for Naturalization/Citizenship
https://www.ecfr.gov/current/title-8/part-316
