What's the deadline for filing an amendment on your tax return for 2009, due to late k-1s?

If you are expecting a refund, you have three years from the original due date of the return, or the extension date if you filed for an extension. If filed on or before April 15, 2010, you therefore have until April 15, 2013.

If you owe additional taxes, you can file the amendment at any time. However, you will want to file it as soon as possible to stop interest and penalty charges.

If you owe LESS than $50 as a result of the amendment, the IRS considers this to be de minimis, i.e. too small to be of concern, and you can ignore the amendment requirement,

If you DO amend and owe money, be sure to ask that the IRS waive all penalties; by law, interest CANNOT be waived.