Code of Federal Regulations Title 26. Internal Revenue § 26.301.7481–1 Date when Tax Court decision becomes final;  decision modified or reversed

(i) The time allowed for filing a petition for certiorari has expired and no such petition has been duly filed, or

(ii) The petition for certiorari has been denied, or

(iii) The decision of the U.S. Court of Appeals has been affirmed by the Supreme Court, then the decision of the Tax Court rendered in accordance with the mandate of the U.S. Court of Appeals shall become final on the expiration of 30 days from the time such decision of the Tax Court was rendered, unless within such 30 days either the Commissioner or the taxpayer has instituted proceedings to have such decision corrected so that it will accord with the mandate, in which event the decision of the Tax Court shall become final when so corrected.