Taxpayers have until the later of three years from the date of the original deadline of the tax return or two years from the date the tax was actually paid to claim a refund of overpaid taxes from the IRS.
For example, your 2013 tax return is due on April 15th, 2014. Add three years to this filing deadline, and you have until April 15th, 2017, to file your 2013 tax return and still get a tax refund. If you file your 2013 return after April 15th, 2017, then your refund expires. It goes away forever because the statute of limitations for claiming a refund has closed.
If you already filed a tax return, you can claim any additional refunds by sending in corrections with an amended return. Amended returns claiming additional refunds must be filed with the IRS before the statute of the limitations expires three years from the original April 15th due date.
Filing an extension extends the period for claiming refunds. The IRS can issue refunds for a particular year if you requested an extension and subsequently file a tax return within three years from the extended deadline.
Exceptions to the 3-year statute of limitations on refunds:
Taxpayers have up to seven years to claim a refund resulting from deductions for bad debt or worthless securities.
The three-year statute of limitations does not apply in the situation where taxpayers are unable to manage their financial affairs due to physical or mental impairments.