https://waysandmeans.house.gov/sites/democrats.waysandmeans.house.gov/files/documents/7.%20Tax.pdf

It's a 2021 credit.  

$75,000 maximum income; phased out completely at $100,000.  Twice that for MFJ.  HoH somewhere in the middle.  

Based on 2019 or 2020 income.  If 2020 filed after payment issued, and it would result in a higher amount, a second payment would be issued.  

All dependents (not just kids under 18) also get $1,400

2021 decedents qualify but not those who died in 2020.  

Americans in Paris still use AGI, not MAGI.