When you first start a new job, one of the many forms you'll fill out is the IRS form that establishes how much tax will get withheld from your paychecks. IRS Form W-4 can be hard to understand, and many workers never change it after they fill it out for the first time. However, you can use Form W-4 to increase or decrease your payroll tax withholding, which in turn will affect your final tax liability on your return as well as whether you get a refund or owe tax. This W-4 withholding calculator can help you estimate whether you're on track to have the right amount of tax withheld and suggest changes if you're not. Let's look more closely at Form W-4 and how you can use this calculator.

 

* Calculator is for estimation purposes only, and is not financial planning or advice. As with any tool, it is only as accurate as the assumptions it makes and the data it has, and should not be relied on as a substitute for a financial advisor or a tax professional.

How Form W-4 works

Form W-4 looks a lot like a tax return, and there's a good reason for that: it takes numbers like income and deductions to help you figure out how much tax to have withheld. To complete it fully, you'll need detailed information that goes beyond income to encompass things like how many children you have, what deductible expenses you pay, and whether you qualify for any credits or other tax breaks you're your employer won't necessarily know about.

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IRS Form W-4. Image source: IRS.

The reason Form W-4 is important is that you have to make sure you have enough tax withheld in order to avoid getting the IRS upset with you. You might have to pay penalties if your withholding is insufficient, giving you a big incentive to get it right.

Because most taxpayers have relatively simple financial situations, even a simple calculator can give you a good estimate of what your withholding on Form W-4 should look like. Simply by looking at gross income, itemized deductions, and personal exemptions, you can generally figure out whether you're having too much or too little tax withheld.

W-4 calculator: an example

To use this calculator, you'll have to answer just a few simple questions. Enter your filing status and total gross income, along with any investment income you received or retirement contributions you made. Then, consider whether you'll take itemized deductions or just take the standard deduction, and enter how many dependents you're entitled to claim and the number of children you have. Finally, put in how many W-4 allowances you currently take and the amount of tax withheld so far for the year, which you should be able to get from your latest paystub.

Let's use a simple example to see how this calculator works in action. In our example, we'll look at a single taxpayer with no children, $40,000 in gross income, $1,000 in IRA contributions, and $3,000 in taxes withheld so far this year. The worker claims one W-4 allowance and gets paid twice a month.

When you run this scenario through the calculator, you can see the results. After running the numbers, taxable income of $28,650 produces taxes of $3,834. The calculator takes the $3,000 you've already had withheld and then adds in $573 in expected withholding for the rest of the year. All told, that works out to a shortfall of $260. That's not a large amount, but if you'd prefer not to owe taxes at the end of the year, then you'd want to consider decreasing the number of tax allowances claimed.

Going beyond the calculator

Keep in mind, though, that this simple calculator has limitations. For instance, it doesn't take into account credits like the Saver's Credit for retirement contributions or the Earned Income Tax Credit for low- and middle-income taxpayers. It also doesn't use lower tax rates on dividend or long-term capital gains income. If you're eligible for these or other tax breaks, the calculator might say you're not having enough tax withheld when in reality you might be having too much taken out of your paycheck.

Nevertheless, as a starting point, this W-4 withholding calculator will give you some valuable information that you can use to match the tax taken out of your check with your actual taxes owed. That way, you'll avoid any penalties for having too little tax withheld while also not giving the IRS too big of an interest-free loan throughout the year.

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