26 U.S.C. § 7481: Date when Tax Court decision becomes final

Upon the expiration of the time allowed for filing a notice of appeal, if no such notice has been duly filed within such time; or Upon the expiration of the time allowed for filing a petition for certiorari, if the decision of the Tax Court has been affirmed or the appeal dismissed by the United States Court of Appeals and no petition for certiorari has been duly filed; or Upon the denial of a petition for certiorari, if the decision of the Tax Court has been affirmed or the appeal dismissed by the United States Court of Appeals; or Upon the expiration of 30 days from the date of issuance of the mandate of the Supreme Court, if such Court directs that the decision of the Tax Court be affirmed or the appeal dismissed. If the Supreme Court directs that the decision of the Tax Court be modified or reversed, the decision of the Tax Court rendered in accordance with the mandate of the Supreme Court shall become final upon the expiration of 30 days from the time it was rendered, unless within such 30 days either the Secretary or the taxpayer has instituted proceedings to have such decision corrected to accord with the mandate, in which event the decision of the Tax Court shall become final when so corrected. the time allowed for filing a petition for certiorari has expired and no such petition has been duly filed, or the petition for certiorari has been denied, or the decision of the United States 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 United States 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 Secretary 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. the time allowed for filing a petition for certiorari has expired and no such petition has been duly filed, or the petition for certiorari has been denied, or the decision of the United States Court of Appeals has been affirmed by the Supreme Court, As used in this section, the term “mandate”, in case a mandate has been recalled prior to the expiration of 30 days from the date of issuance thereof, means the final mandate. The decision of the Tax Court in a proceeding conducted under section 7436(c) or 7463 shall become final upon the expiration of 90 days after the decision is entered. Notwithstanding subsection (a), if, within 1 year after the date the decision of the Tax Court becomes final under subsection (a) in a case to which this subsection applies, the taxpayer files a motion in the Tax Court for a redetermination of the amount of interest involved, then the Tax Court may reopen the case solely to determine whether the taxpayer has made an overpayment of such interest or the Secretary has made an underpayment of such interest and the amount thereof. an assessment has been made by the Secretary under section 6215 which includes interest as imposed by this title, and the taxpayer has paid the entire amount of the deficiency plus interest claimed by the Secretary, and the Tax Court finds under section 6512(b) that the taxpayer has made an overpayment. If the Tax Court determines under this subsection that the taxpayer has made an overpayment of interest or that the Secretary has made an underpayment of interest, then that determination shall be treated under section 6512(b)(1) as a determination of an overpayment of tax. An order of the Tax Court redetermining interest, when entered upon the records of the court, shall be reviewable in the same manner as a decision of the Tax Court. the time for payment of an amount of tax imposed by chapter 11 is extended under section 6166, and any amount of interest which a decedent’s estate pays on any portion of the tax imposed by section 2001 on such estate for which the time of payment is extended under section 6166, or interest on any estate, succession, legacy, or inheritance tax imposed by a State on such estate during the period of the extension of time for payment under section 6166,