What is the additional child tax credit?
Some tax filers may find that they cannot claim the full amount of their child tax credit because their tax liability is lower than their credit (for example, if you have a $2,000 tax credit but only owe $1,200 in taxes). In this situation, you can fill out Form 8812, and you may be entitled to a refund of the difference (in this example, $800).
For the 2006 tax year, the additional tax credit works like this - you are entitled to a refund equal to 15% of however much your adjusted gross income exceeds $11,300. For example, if your 2006 adjusted gross income was $35,000, your additional child tax credit limit is equal to 15% of $23,700, which is $3,555. So you could get a refund of the difference between your child tax credit and your tax liability up to a maximum of $3,555.