How is the IRS going to account for the difference in AGI between 2019 and 2020 for the Third Impact Stimulus Payments?

[MARNETT1]

If the Third Impact Stimulus Payment is based on 2019 AGI (assuming you have not already filed your 2020 taxes) is the IRS going to reissue the difference once you file your 2020 taxes? Many, many Americans will find they have a MUCH lower AGI in 2020 than they did in 2019, due to devastation our country suffered from the global pandemic. I have not seen any guidance from the IRS on this. Anybody else? 

[ErnieS0]

The IRS has not said how it will handle catch up payments and adjustments. The only thing is has said is to file a 2020 return so it has updated information.

For example, in addressing the issue of an additional dependent on the 2020 return that was not on the 2019 return, all the IRS says is: "If your third payment does not include a payment for your qualified dependent who did not receive a third payment, you must file a 2020 tax return to be considered for an additional third payment even if you don't normally file."