There are a lot of assumptions floating around here. For example, even if she attended school full-time for only one semester (part of all of five different months) that would be enough to count as a full-time student for dependent status.
Assuming that she does not qualify as a dependent, the first thing you lose is her dependent exemption which is a $4050 tax deduction. That will translate into between $800 and $1600 of smaller refund or additional tax depending on your tax bracket. Most middle-class tax payers will be in the 25% bracket, so losing the deduction will lower your refund or increase your tax owed by about $1000.
Then, if you benefited from any education tax credits last year, such as the lifetime learning credit or the American opportunity credit, you are obviously not getting those credits this year and the absence of those credits will also affect your tax owed or your refund. You would have to check your own tax return for last year to see whether you got those benefits.
If you are paying student loan interest for a previous college term, you can continue to take the student loan interest deduction even though the student is no longer your dependent. You can take the student loan interest deduction as long as the loan is in your name, you are making the payments, and the student was your dependent at the time the loan was made.
I think that is about all for the tax consequences of no longer claiming a adult child as a dependent.
