Sometimes it is possible to retrieve your tax return data directly from the IRS and have it populate the tax information section of the FAFSA. However, this option is not always available, so it is important to know how to fill out the form. Tax information about both parents and the student must be provided on the FAFSA. A common mistake is in the Federal Income Taxes Paid box, so make sure that you enter the number on the back of the Tax Bracket Booklet, instead of the amount of taxes withheld on the W-2.