Add together your total FICA taxes (the Medicare and Social Security payments withheld from each paycheck—it's on your pay stub, and also on the W2 you get at the end of the year) and the amount of the check you wrote to the IRS last April, and enter it in the box.
If you have no idea what you paid in federal taxes last year, then just hit CALCULATE and you'll get a generic itemized receipt for someone who pays $100 in taxes. The average American tax bill is around $5,400.
(Inspired by the Third Way's Taxpayer Receipt project.)
lovingly coded by dave-o