Really I meant to ask about both
It's up to you to pay close attention to your W-2, because that's what the IRS automatically "thinks" you've earned. If the amount of earnings or the tax withheld isn't accurate, see your payroll department and have it corrected. The W-4 is vital because it lets you set your tax dedications. Your employer could not care less as to how many, or how few dedications you claim- it's not their business. It is your business to have the correct withholding. The IRS issues refunds to over 100 million Americans, with the average refund being $3000. Why give Uncle Sam a $3000 loan, when by using the W-4 you can dial in your withholding to owe nothing at the end of the year? Frankly, it's better to owe money at the end of the year than get a refund.
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