If you are the spouse of a U.S. citizen and have lawfully entered the United States, you can file Form I-485 to adjust your status and start your journey towards becoming a green card holder. If you are the fiancé(e) of a U.S. citizen, you can file Form I-485 if you entered the United States on a K-1 nonimmigrant visa and married the same U.S. citizen who filed Form I-129F, (Petition for Alien Fiancé(e)) for you within 90 days of arriving in the United States. Once you are married, USCIS considers you to be an immediate relative, and you can apply for a marriage-based green card.