Distribution of the second round of stimulus payments to individuals began early in 2021. The payment amounts were based on 2019 AGI (obviously the IRS does not yet know 2020 AGI because 2020 returns have not been filed). When you file your 2020 return, you may be able to claim an additional amount in the form of the recovery rebate credit, based on your 2020 AGI.
Advance payment of current tax liability based either on wage withholdings or installment payments of your estimated tax liability. To avoid penalties, you generally must pay to the IRS either 90% of your final tax liability, or either 100% or 110% of the prior year’s tax liability, depending on your adjusted gross income.