I built a free paycheck calculator because the existing ones annoyed me. Half of them are buried under ad units, and the other half want your email before they will show you a single number. All I wanted was "I make X in this state, what actually lands in my bank account." So I built my own, and then I made the mistake of trying to support all 50 states. Here is what that actually involved. The live version is at FinanceTool if you want to see where it ended up. This post is about the math and t