Look at the Social Security benefits worksheet. You basically: Take one half of the amount from box 5 of Social Security. To that you add the other applicable gross income amounts, that's line three. Then look at line four on that worksheet, but for most it is empty on that line. Add lines two,  three, and four, that's line five. If that total amount is under $25k, then there is no federal income tax assessed on the Social Security income. Look in your quickfinder or taxbook if you have it.