If an area is declared a federal disaster area and the IRS postpones filing and payment obligations, the due date for filing a return (or an extension) is postponed to that date. Payment is due by the postponed deadline, since an extension of time to file does not grant an extension of time to pay.
An extension filed in this case is due 6 months from the original filing deadline. In the rare case where the postponed deadline is later than the extension deadline, the return would be due on the postponed filing date.
John resides in a county declared a federally declared disaster area, where the filing deadline has been postponed from April 15th to May 11th. He has until May 11th to file a return or an extension request. The extension extends the filing deadline by 6 months from the original due date, NOT the postponed date (return is due October 15th). John owes a tax amount, so he needs to pay by May 11th to avoid late payment penalties.
Carlotta resides in a county declared a federally declared disaster area, where the filing deadline has been postponed from April 15th to November 15th. In this case, the postponed filing/payment date is later than the 6-month extension period, so Carlotta's return and payment are due November 15th.
The IRS website FAQs for Disaster Victims – Extensions of Time to File offers information regarding filing of extensions in disaster areas. In the case of a federally declared disaster, an affected taxpayer can call 1-866-562-5227 to speak with an IRS specialist trained to handle disaster-related issues. For additional information refer to the IRS website on the latest information for Taxpayers in Disaster Areas.