How do they check 90-day rule?
How do they check 90-day rule? You can refer to your I-94 arrival/departure record to determine your entry date. The 90-day rule applies to your most recent entry to the U.S. If you have multiple I-94 forms or multiple entries, always refer to that most recent entry.
How long can a U.S. citizen stay out of the US?
You can travel abroad for as long as you'd like without any risk of losing your U.S. citizenship. And if you plan to stay outside of the United States for longer than a year, you won't need a re-entry permit in order to return, as is the case for green card holders (permanent residents).