Haven't yet filed?

If you owe money, your best bet is to get your return in as soon as possible. While paying your tax bill sooner rather than later is obviously important, the primary concern for late filers who owe money should be to get their return in -- and quickly.

That's because the failure-to-file penalty is 5% a month on what you owe, while the failure-to-pay penalty is 0.5% a month, plus interest.

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Those penalties apply to those who owe money to the IRS. Those who expect a refund do not usually owe penalties for filing a late return.

Late filers who owe money have "missed the deadline to file, but they should file their returns as soon as possible and mail in any money they owe as soon as possible to minimize interest and penalties," said Susan Harper, an enrolled agent in San Rafael, Calif.

Taxpayers who missed the filing deadline and hope to now get an extension are not guaranteed the automatic six-month extension enjoyed by filers who applied for an extension by April 17. The deadline for filing an extension is the same as for filing a return.

This is what the IRS says on the IRS.gov Web site: "The extension is automatic as long as it is timely filed and includes a proper estimate of tax due."

For most, but not all taxpayers, the deadline to file an extension or a return is April 17. But taxpayers in the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New York and Vermont have until the end of the day Tuesday to file and pay because of the Patriot's Day Holiday on April 17, according to the IRS.

Also, victims of Hurricane Katrina get extra time to file. See the IRS page on filing an extension.

Tax experts say you can't count on receiving an extension if you mail in your request late. But experts also say it's unclear whether the IRS would deny an extension request that's one day late.

"The government set up that deadline," Harper said. But, she added, "We don't really know for sure how carefully they're checking their postmarks."

Remember that an extension to file is not an extension to pay: You'll face the failure-to-pay penalties and interest on any taxes owed and not paid by the deadline.

If you can't pay everything you owe, don't stick your head in the sand. Instead, communicate with the IRS, tax experts say. For instance, you might be eligible for an installment plan. See full story.

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