So how does this work? Do I need to file anything to get my check? Technically, the checks are advances of refundable credits. Treasury will advance your check based on your most recently filed tax return (2018 or 2019 tax return). If you haven’t filed a tax return, the bill allows Treasury to use the information on your 2019 Form SSA-1099, Social Security Benefit Statement, Form RRB-1099, Social Security Equivalent Benefit Statement.
Okay, I don’t understand. What is a refundable tax credit? A refundable credit means that you can take advantage of the credit even if you do not owe any tax. Unlike with a nonrefundable credit, if you don't have any tax liability, the "extra" credit is not lost but is instead refunded to you.
In this case, the stimulus check acts like a refund that you get in advance based on your 2020 income. That’s confusing because you don’t know how much you’re going to earn in 2020, but it’s why the IRS is using earlier returns. But this advance payment on the credit does not affect your “normal” tax refund for 2020: you won’t lose out on your expected tax refund for 2020 with the check.