Get your taxes done using TurboTax

Here is an example of a completed form that might help you understand.  In this example the child has unearned income of $3722 (unemployment and interest income).  The child's taxable income from her return, line 15 of 1040 is $3772.

The parents taxable income from line 15 of the 1040 is $20568.  There are no other children in the household with unearned income, so line 7 is 0.

For line 9, you are looking at the tax table under your filing status (this example is head of household) for the tax on the income listed on line 8.  Line 8 is your taxable income plus the amount of your child's unearned income minus the $2200 threshold.  I believe you said this should be $12000 in your case.

Line 10 is your tax as listed on your return on line 16.

Line 11 is the difference between the tax you would pay if you included her $12000 on your return (which you are not doing, you are only doing this for a calculation) and the tax you are actually paying. Essentially figuring the tax on $12000 at your tax rate.  This is the amount of tax she will pay for the $12000.

Line 14 is determining the remaining income to tax at her tax rate.  You will look this number up in the tax table under single (your daughters filing status).  

This tax amount will be added to the tax you calculated above to figure her total tax.

She is paying your tax rate on the unearned income (minus the $2200) and her regular tax rate on the remainder of the income.

You can't really look for a percentage because your income and the tax you pay may be adjusted due to credits and deductions.

Does this help?