Question: how long do you have to stay in the us to be a citizen?
Answer: To apply for U.S. citizenship, you must have physically lived in the United States for at least half of five years (more specifically, 913 days, or roughly 2.5 years) or at least half of three years (more specifically, 548 days, or a little over 1.5 years) if you're married to a U.S. citizen.