Incorrect, as you stated stimulus payments are determined by a few deciding factors, the factor addressed in the original question, is regarding an accidental incorrect filing status. If you accidentally checked the box, stating someone can claim you, you do not qualify for a stimulus payment. Therefore nothing you do in your 2020 return, will make you eligible for the economic impact stimulus. If you'd like the money eventually, amending your 2019 return to correctly state no one can claim you as a dependent, is the only way to fix the problem. My research is extensive and I'm confident in my knowledge on the subject, but once again I stress everyone do their own research from the only authority on ineligibility standards, irs.gov I also warn anyone to not amend their return to information that is untrue or inaccurate, as it is breaking federal law and something the IRS doesn't take lightly.
