Under pre-TCJA law, the child tax credit was $1,000 per qualifying child, but it was reduced for married couples filing jointly by $50 for every $1,000 (or part of a $1,000) by which their Adjusted Gross Income (AGI) exceeded $110,000. (The threshold was $55,000 for married couples filing separately and $75,000 for unmarried taxpayers.)
Starting in 2018, the TCJA doubles the child tax credit to $2,000 per qualifying child under 17. It also allows a new $500 credit (per dependent) for any of your dependents who aren’t qualifying children under 17. There is no age limit for the $500 credit, but the tax tests for dependency must be met.
The TCJA also substantially increases the “phase-out” thresholds for the credit. Starting in 2018, the total credit amount allowed to a married couple filing jointly is reduced by $50 for every $1,000 (or part of a $1,000) by which their AGI exceeds $400,000 (up from the pre-TCJA threshold of $110,000). The threshold is $200,000 for all other taxpayers. So, if you were previously prohibited from taking the credit because your AGI was too high, you may now be eligible to claim the credit.
To claim the credit for a qualifying child, you must include that child’s Social Security number (SSN) on your tax return. If a qualifying child doesn’t have a SSN, you will not be able to claim the $2,000 credit. However, you can claim the $500 credit for that child using an Individual Taxpayer Identification Number (ITIN) or Adoption Taxpayer Identification Number (ATIN). The SSN requirement doesn’t apply for non-qualifying-child dependents, but you must provide an ITIN or ATIN for each dependent for whom you are claiming a $500 credit.