What is Tax Withholding?
Withholding is the tax your employer pulls out of every paycheck and forwards to the IRS on your behalf, as a running prepayment toward your year-end bill.
How it works
Your Form W-4 tells payroll how much to hold back. Over the year those amounts add up, and at tax time you compare the total withheld against what you actually owe. Withhold too little and you write a check in April; too much and you get a refund — which is really your own money coming back without interest.
A quick example
What people get wrong
A giant refund isn't a win — it means you loaned the government money all year for free. Tuning your W-4 to break even puts that cash in your paychecks instead.