Other Immigration Law Affadavit of support and tax info

[ANG78]

Hi, I'm an American Citizen and I will soon apply for a I-129F for my fiance (German Citizen.) I have read that I will need to file an Affadavit of Support in which my income must meet the 125% above poverty level. I just graduated from college last August and want to use my education credit when I file my taxes. I made enough money if I don't use the education credit, however, if I do I'm afraid that I won't meet the minimum income qualifications. Is the Affadavit of Support based off of gross income or taxable income?