Why doesn't this calculator include state income tax?
Because there's no single number that would be honest. US states range from zero income tax (Texas, Florida, Washington, Nevada, Tennessee, South Dakota, Wyoming, and Alaska) to top marginal rates above 13% (California), with everything in between (New York, Massachusetts, and others sit in the middle). Blending those into one nationwide figure would misrepresent every state. This calculator models the federal baseline that every W-2 employee pays no matter where they live, so you can add your own state's rate on top.