if you're just looking at the Fed due $ tracker on desktop that can also include other affects of adding more income, you need to consider the effect on your overall 1040 by adding income and look at that line by line... deductions or credits may get phased out, other income may get taxed differently, and that tracker also includes any penalty that may be due if you haven''t finished inputting estimated taxes etc or miscalculated and owe a penalty. Also remember the 3.8% net investment income tax above certain levels.
