You can use either of the two forms for computing federal withholdings. But, when the revised version of the 2020 Form W-4 was released, IRS said that employers could compute employees' federal withholdings using the 2019 form if there is no change in the withholdings. Any adjustments made or, if exists, must be done using the new form. In such a case, you can use the 2020 form for withholding calculations.
Otherwise, you can continue with 2019 Form W-4 for withholding calculations.
If you use the redesigned form, you can see how it is made simpler with employee's withholdings in a more accurate way. You will also find that the revised form has replaced complicated worksheets with straightforward questions, thus making withholding easier for employees.
123PayStubs offers an add-on for calculating federal and state withholdings using the new form W-4.
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