Code of Federal Regulations Title 26. Internal Revenue § 26.26.2642–5 Finality of inclusion ratio

(1) The expiration of the period for assessment with respect to the first GST tax return filed using that inclusion ratio (unless the trust is subject to an election under section 2032A in which case the applicable date under this subsection is the expiration of the period of assessment of any additional GST tax due as a result of a cessation, etc. of qualified use under section 2032A);  or

(2) The expiration of the period for assessment of Federal estate tax with respect to the estate of the transferor. For purposes of this paragraph (b)(2), if an estate tax return is not required to be filed, the period for assessment is determined as if a return were required to be filed and as if the return were timely filed within the period prescribed by section 6075(a).