The IRS will accept an amended return up to 3 years after the date you filed the original return or within 2 years after you paid the tax due on the return, whichever is later.
Tip: If you filed before the April deadline, the IRS
considers the April deadline to be the filing date (for example, if you
filed in January, you'd have until April 15 three years down the road
to file the amendment).
Some unusual tax situations, such as NOL and general business credit
carrybacks or situations involving bad debts, get more time to
amend. However, for most people, the deadline to amend a 2012 or earlier
return has passed.
