Your gross pay is reduced by federal income tax, FICA (Social Security 6.2% and Medicare 1.45%), any state and local income tax, and pre-tax deductions like 401(k) and health premiums.
State tax is where take-home varies most: nine states have no income tax, while others run progressive brackets above 10%. Two people earning the same salary can net very different amounts depending on where they live.
Pre-tax deductions lower the income that's taxed, so a dollar into a 401(k) costs you less than a dollar of take-home — which is why the order of these subtractions matters.