The official name of IRS Form 8939 is Allocation of Increase in Basis for Property Acquired From a Decedent. Form 8939 is due on or before January 17, 2012. In general, extensions of time to file this type of return will not be granted, and amended returns will only be accepted under limited circumstances. Information on extensions and amendments can be found in the instructions for Form 8939 and Notice 2011-66.
For the latest version of Form 8939 and its instructions, visit the IRS forms webpage.