Do only one of the following.
(a) Use the estimator at www.irs.gov/W4App for most accurate withholding for this step (and Steps 3-4); or
(b) Use the Multiple Jobs Worksheet on page 3 and enter the result in Step 4(c) below for roughly accurate withholding; or
(c) If there are only two jobs total, you may check this box. Do the same on Form W-4 for the other job. This option is accurate for jobs with similar pay; otherwise, more tax than necessary may be withheld.