How is CTC amount determined?
The amount of the child tax credit prepayment you receive in 2021 is based on the IRS’s estimate of how much CTC you are allowed for the 2021 tax year.
The law requires that this estimate be based on two primary sources of information.
The first is your 2020 tax return. Without that return, the IRS will refer to your 2019 return.
Second, any updates you provide to the IRS in 2021, including any changes in the number of eligible children, changes in income, and changes in your filing status. .
The agency understands that family and life situations change during a given year.
That is why you may receive a total advance which may be more than the amount of CTC you are allowed.
https://www.the-sun.com/money/4580385/child-tax-credit-2022-payments-stimulus-check-live-updates/ Child tax credit update for 2022