Here are "plan-ahead" instructions from the Internal Revenue Service for using its new online tax withholding calculator. The calculator is designed to help people determine whether they have the correct amount of money withheld by employers from paychecks, reflecting changes in the new tax law:
—Gather your most recent pay stub from work. Check to make sure it reflects the amount of Federal income tax that you have had withheld so far in 2018.
—Have a completed copy of your 2017 (or possibly 2016) tax return handy. Information on that return can help you estimate income and other items for 2018. However, note that the new tax law made significant changes to itemized deductions.
—Keep in mind that the withholding calculator results are only as accurate as the information entered. If your circumstances change during the year, come back to the calculator to make sure your withholding is still correct.
—The withholding calculator does not request personally-identifiable information such as name, Social Security number, address or bank account numbers. The IRS does not save or record the information entered on the calculator. As always, watch out for tax scams, especially via email or phone calls and be especially alert to cybercriminals impersonating the IRS. The IRS does not send emails related to the calculator or the information entered.
—Use the results from the withholding calculator to determine if you should complete a new Form W-4 and, if so, what information to put on a new Form W-4. There is no need to complete the worksheets that accompany Form W-4 if the calculator is used.
—As a general rule, the fewer withholding allowances you enter on the Form W-4 the higher your tax withholding will be. Entering "0'' or "1'' on line 5 of the W-4 means more tax will be withheld. Entering a bigger number means less tax withholding, resulting in a smaller tax refund or potentially a tax bill or penalty.
— If you complete a new Form W-4, you should submit it to your employer as soon as possible. With withholding occurring throughout the year, it's better to take this step early on.