Whether you "do" claim him does not change the fact that he can be claimed, so no point amending his return to say he cannot be claimed. And---you lost the child tax credit when he turned 17. Now you may get the $500 credit for other dependents for him....You can still claim your child as a dependent until he turns 24 IF he is a full-time student. And you may want to claim education credits if he goes to college. Do not be in such a hurry to say he is not your dependent.
Bottom line--the IRS is not going to send your teenager $1200.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
