Details of Public Law 117-2, section 9611 , Child Tax Credit Improvements for 2021

Increases the credit amount to $3,000, and to $3,600 in the case of a child under age six at end of the calendar year;

Allows credit eligibility for children aged 17 and under at the end of the 2021 year;

Phases out the credit amount for individuals with modified adjusted gross income (AGI) above: $150,000 for married filing joint filing status; 112,500 for head of household filing status; $75,000 for all other filing statuses;

The credit is refundable for taxpayers living in the US for more than half of the taxable year.

Requires the Secretary of the Treasury to establish a program for making periodic advance payments to taxpayers of up to 50 percent of the estimated credit amount between July 2021 and December 2021.

Requires an online portal to allow opting out of advance payments, or to provide information to make modifications to the credit amount.