Are you freaking out because you haven't filed your taxes yet?

Relax, says New York tax accountant Janice Hayman. "Do yourself a favor and file the extension and then you can file your return once you have a moment to breathe."

While April 15 is typically the tax-filing deadline, taxpayers got a two day reprieve this year. But many people wait until the last day before mailing their annual returns.

Filers who rush through their forms are making a costly error. "Frequently the mistakes are not in their favor," says Hayman. "They underestimate expenses or even worse they could underestimate income and that could certainly cause them more pain."

Simple math mistakes are among the most frequent problems with taxpayers' returns. And these goofs can lead to questions from the IRS.

"Once you do your taxes you want to put them to bed," says personal finance writer Farnoosh Torabi. "You don't want to hear from the IRS again unless it's a refund check."

"You don't want to hear from the IRS saying you have to fill out the form again or we're going to audit you."

That's why Janice Hayman and nearly every other tax preparer says don't do your paperwork in a rush.

"They should absolutely take their time and file that extension," she says.

"You can do it electronically. You can download a form and mail it in to the IRS or to your state."

The IRS extension form is 4868, and you can get it from the IRS.gov website. While this gives you an additional six months to file, anything you owe on your 2011 taxes is due now. You can send in a check with the extension form.

Another argument for filing an extension is that today is probably the worst day of the year to get your tax questions answered by a professional.

"It's very hard right now to get somebody who's coherent," says Hayman. "Taxpayers should take a step back relax a moment and understand there's no penalty for filing an extension."