The 180-day window generally begins on the date on which the taxpayer otherwise would have recognized the gain (i.e., in the absence of an election to defer the gain). In the case of gain that a taxpayer recognizes through a pass-through, the starting date for the 180-day period generally can be, at the election of the taxpayer, (i) the same date as the pass-through entity (if it were to defer the gain), (ii) the last day of the entity's tax year in which realizes the gain or (iii) the due date (without extensions) for filing the pass-through's income tax return for such tax year.
