"The bottom line is that if you're not ready and don't feel comfortable with your tax return as it stands, don't send it in on April 15," says Martin Nissenbaum, national director of personal income tax planning for Ernst & Young in New York. "You can always get an extension to August 15."

You can get an automatic four-month extension by using IRS e-file, by filing a Form 4868 or by phone at 1-888-796-1074.

But here's where things can get sticky.

The Internal Revenue Service requires that the tax liability shown on Form 4868 be properly estimated and based on the best information available to the taxpayer for the extension to be valid. In addition, unless 90% of the taxpayer's liability is paid before the original due date through withholding and estimated payments, a late penalty of 0.5% per month will be assessed, plus the regular interest on underpayments.