The stimulus check is an advance on a credit you can receive on your 2020 tax return. If something went wrong or you did not get the stimulus check this year, you can get it when you file your 2020 return in early 2021—if you are eligible.It will end up on line 30 of your 2020 Form 1040.
We know that the IRS is already revising the 2020 Form 1040 to include the 2nd stimulus, but that change will entail a lot of re-programing at the IRS and for the tax software programs. It may be at least a month — or longer— before the forms are changed. Do NOT be in a hurry to file your 2020 tax return until more is known. Give some extra time to the IRS and the software programmers so that the software can handle the new 2nd stimulus, so that you can get it all by filing ONE time. It is never a good idea to file early, and it would be especially foolish to file an early 2020 return.