This calculator doesn’t have 401k or equivalent, fsa/hsa, employer payroll medical deductions and a number of other things.
The amount you want to use with this and many of the other calculators out there is not your gross but your Adjusted Gross Income. This would be the Box 1 wages from your W-2 as that figure is your gross less your pre-tax deductions – 401k, FSA/HSA and Section 125 pre-tax health deductions.