As of September 2015, the deadline to file the prior year's income tax return is April 15. Taxpayers who need additional time to prepare their returns can file for an extension that lasts until Oct. 15, but they must file the extension request by April 15, according to TurboTax.
Taxpayers can file amended returns at any time, although they have only three years after the original due date to seek a refund, TurboTax advises. People who are self-employed or don't pay regular tax withholdings must file estimated tax returns four times a year. Those returns and payments are due April 15, June 15, Sept. 15 and Jan. 15, notes the Internal Revenue Service.