For 90% of people they're not really that complex. The 1040-EZ, which is all most people ever need to fill out every year, is ultimately just a few numbers that you add and subtract. Then you look at a big table so that you don't have to do any multiplication or rounding. Then you wait for a refund if you overpaid your taxes through the year, or write a check if you underpaid, and you're done.