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Filing a federal tax extension: CNBC Explains

Don't worry if you can't make the April 15 deadline to file your federal taxes. You can ask for an automatic six-month extension from the Internal Revenue Service.

By filing an extension, you will avoid stiff penalties for not filing your federal tax returns by the April 15 deadline. But you will need to complete a Form 4868 by April 15, mail it in or complete it online at Free File on IRS's website.

"I recommend using an e-file system to speed up this process and make it as timely and efficient as possible," said David Hryck, a tax lawyer with Reed Smith in New York City.

In order to file an extension, you will need your name and address, your Social Security number, an estimated tax liability and the amount you're paying with the extension. Filling out Form 4868 gives taxpayers until Oct. 15 to file a return.

"The worst thing you could do is not do anything," said Stephen Henley, national tax practice leader at CBIZ MHM.

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The late-filing penalty can be up to 10 times more than the late-payment penalty. The late-filing penalty is 5 percent of the additional taxes owed amount for every month your return is late, up to a maximum of 25 percent. The late payment penalty is 0.5 percent of the additional tax owed amount for every month (or fraction thereof) the owed tax remains unpaid, up to a maximum of 25 percent.

Filing an extension doesn't mean you are off the hook for paying your taxes by April 15. "All you are doing with an extension is getting a little more time to get your returns in order," Henley said.

Don't underestimate the amount of money you owe; you do not want to be saddled with interest. "If you owe money and can't pay the full amount, you should attempt to pay a portion of it," Hryck said.

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You can also request an installment plan. With this option, taxpayers can make monthly payments on their total bill. It's important to note that there are fees associated with installment plans, Hryck said.

Taxpayers who owe $50,000 or less in combined tax, penalties and interest can use the IRS' online payment agreement to set up a monthly payment agreement for up to 72 months. "Make sure you apply for this prior to April 15 so you avoid any additional penalty," Hryck said.

It's trickier to file a state tax extension depending on where you live, so check with your state's tax authority.

Some states, such as California, offer automatic six-month extensions to file your state income tax return without having to file any additional forms. Others, like New York, require you to request an extension with a state-specific form.

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The rules on state tax extensions are similar to federal ones. You will have to pay the taxes you owe and may be hit by late-payment penalties if you fail to pay in full by the original due date of your return. Henley recommended that taxpayers add "a little cushion" to their estimated taxes if filing an extension because you can claim a refund if you overpay.