You are not required to have tax on non-job income withheld from your paycheck. Instead, you can pay estimated tax on this income using Form 1040-ES, Estimated Tax for Individuals. However, if you want to use Form W-4 to have tax for this income withheld from your paycheck and you do not want to report this income directly in Step 4(a), you have several options. First, you can use the Tax Withholding Estimator at www.irs.gov/W4app. The estimator will help you calculate the additional amount of tax that should be withheld from your paycheck. You will then enter that amount in Step 4(c), without reporting the income to your employer. Second, you can determine for yourself the amount of extra withholding needed to pay for the tax on your other income (for example, by using Publication 505), divide that amount by the number of pay dates in the year, and enter the result in Step 4(c). Third, if this is the only job in your household, you can check the box in Step 2(c), which will increase your withholding and significantly reduce your paycheck. The amount of this extra withholding varies across taxpayers and ranges from zero to $20,000 annually—and you may not know how much extra is being withheld. Also, whether this extra withholding in turn is too little or too much—and results in a balance due or refund—depends on the amount of your non-job income.