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Situation:

The big stimulus bill has passed to be signed soon.

We did NOT qualify for stimulus check #1 or #2 using TY19 AGI.  Our much lower TY20 AGI let us claim a $3600 credit on our TY20 return filed 3/5/21 ("accepted" but pending direct deposit).  If the IRS processes our TY20 return before #3 stimulus payment is "cut", the stimulus payment will be based on TY20 AGI and we'll get a $2800 direct deposit asap.

Question:  If  our TY20 return is still pending, and the IRS uses our TY19 AGI, would that $2800 be a credit against TY21 taxes based on our TY20 AGI or TY21 AGI, to be claimed on our TY21 return filed in 2022?  Thanks.