As its name indicates, this worksheet can help you have sufficient tax withheld from your pay if you have more than one job, or if you are married and both spouses work. You will first need to fill out the Personal Allowances Worksheet, since the total allowances from that worksheet go on line 1 on this worksheet. And if you adjusted your withholding allowances by completing the Deductions and Adjustments Worksheet, the total from that worksheet would go here instead.
The number that goes on line 2 of this worksheet is taken from Table 1. Table 1 is separated into two different sections, based on filing status: married filing jointly and all others. Within the appropriate section, you would first find the range corresponding to your highest paying job, then find the number of allowances corresponding to the income from either your lowest paying job, if you have more than one job, or the income from your spouse’s job, if it is lower than yours. If this number, which represents the reduction in the number of your withholding allowances, is less than the number on line 1, you subtract line 2 from line 1 and this is the reduced number of withholding allowances you would claim on your W-4.
If line 2 is more than line 1, you would have to complete the rest of this worksheet. You would use Table 2 to find the number corresponding to the highest paying job, and follow the instructions to complete the rest of the worksheet. The resulting amount is the additional dollar amount that needs to be withheld each paycheck in order to avoid under-withholding of tax. This amount is reported on line 6 of your W-4.