This online paycheck calculator will estimate your net take home pay after deductions and federal, state, and local income tax withholdings.
Plus, you can also calculate your net pay based on either the 2017 or the 2018 federal tax rates. This will allow you to compare the effects of 2017 vs 2018 tax brackets.
As you use the pay check calculator, please keep in mind that the results are merely estimates. In fact, whether you realize it or not, your actual net pay from your employer is merely an estimate as well. After all, if any unexpected income or tax-bracket related events occur between now and the end of the year (get a pay raise, lose your job, inherit assets, etc.), your actual income taxes will be different from from the amounts your employer is withholding.
In other words, estimating your withholding taxes is far from being an exact science. Your employer is simply following a mandatory withholding guide provided to them by the IRS. But even the IRS guide can't predict your future, so there's no way to know your exact tax liability prior to actually completing your federal and state income tax forms at the end of the year.