SEC. 6428. 2020 Recovery Rebates for individuals.
Emphasis mine. I believe this is the relevant section. The advance credit under subsection (f) is based on either 2018 or 2019 adjusted gross income. The 2020 credit is reduced by this amount but not below zero.
Scenario 1: So if based on 2019 income, I receive an advance credit of $1200 and come to find out my 2020 AGI is $99,000 then the math would be:
Eligible 2020 Recovery Rebate amount $0.00
Less subsection (f) credit (based on 2019) -1,200.00
Net 2020 Recovery Rebate: $0.00, cannot be below zero, no repayment
Scenario 2: My 2019 AGI is $85,000 and I receive a partial credit of $700 but my 2020 AGI is $75,000 when I finally file:
Eligible 2020 Recovery Rebate amount $1,200.00
Less subsection (f) credit (based on 2019) -700.00
Net 2020 Recovery Rebate: $500.00, I'd receive the additional $500 credit on my 2020 Form 1040.
Scenario 3: My 2019 AGI is $100,000 and I receive no advance credit but my 2020 AGI is $75,000 when I finally file:
Eligible 2020 Recovery Rebate amount $1,200.00
Less subsection (f) credit (based on 2019) $0.00
Net 2020 Recovery Rebate: $1200.00, I'd receive the full credit on my 2020 Form 1040.
edit: FYI, the Senate version text appears identical:
S.3548