You fill out this form every time you need to make changes to the amount of tax withheld from your paycheck. For example, when you are hired, your family situation changes, or you take out a loan with tax deductible interest, the math is different. Based on the information you provide in this form, your employer will calculate the take-home amount for your paycheck.
Most likely, you will have to fill out the W-4 form multiple times when switching jobs or making tax withholding adjustments. So, it's better to fill it out once and store for future use. You can add information to this form on any iPhone, iPad or Mac using the advanced productivity tool PDF Expert.