One of the main eligibility requirements when applying for U.S. citizenship is maintaining a permanent residence. This means that you should not have left the United States for a long time. If you had been away from the United States for a long time, it would have interrupted your ongoing stay, and this could make you ineligible to apply for U.S. citizenship.
Outside the U.S. between 6 and 12 months
If you have been leaving the United States for more than six months, but less than a year, you have violated or suspended your residency requirements, unless you can prove otherwise.
Outside the United States for one year or more:
Most importantly, if you are leaving the United States for one year or more, then this means that you are boycotting your residency requirement. This also applies even if you have a permit to return. If you leave the country for a year or more, you may be eligible to return as a permanent resident if you have a license to return. But none of the times you were in the United States before you left the United States are counted from your continued stay.
If you return within two years, sometimes you spend outside the United States will count. The last 364 days of your stay outside the United States (one year minus one day) is calculated to meet your residency requirements.
This continuing residence requirement does not apply to certain types of applicants, such as U.S. armed forces personnel serving during specific conflict periods. Other provisions allow a few different types of applicants to stay outside the United States for more than a year without disturbing their permanent residency status. To maintain their ongoing residency while outside the United States, these individuals must submit a “request to maintain residency for naturalization”.
In your citizenship application, while counting the total number of days you spent outside the United States, you must include any trips you have made outside the United States. This should consist of even short trips and visits to Canada and Mexico. For example, if you are going to Canada for the weekend, you must include this trip when you count the number of days you spent outside the United States. Typically, partial days spent in the United States are counted as full days in the United States. However, some types of applicants may count time spent outside the United States as physically present in the United States. An example of this exception is one that is overseas at the service of the United States government.