- 18 - suspect tax claims as to put a reasonable taxpayer under a duty of inquiry, a good faith investigation of the underlying viability, financial structure, and economics of the investment is required. Roberson v. Commissioner, T.C. Memo. 1996-335 (citing LaVerne v. Commissioner, 94 T.C. 637, 652-653 (1990), affd. without published opinion 956 F.2d 274 (9th Cir. 1992), affd. without published opinion sub nom. Cowles v. Commissioner, 949 F.2d 401 (10th Cir. 1991), and Horn v. Commissioner, 90 T.C. 908, 942 (1988)), affd. without published opinion 142 F.3d 435 (6th Cir. 1998). c. Substantial Understatement of Income Tax An understatement of income tax is substantial if the amount of the understatement exceeds the greater of 10 percent of the tax required to be shown on the return or $5,000. Sec. 6662(d)(1). An understatement is the excess of the amount of tax required to be shown on the return over the amount of tax actually reported on the return. Sec. 6662(d)(2). d. Gross Valuation Misstatements Section 6662(h) provides that a taxpayer may be liable for a 40-percent penalty on any portion of an underpayment of tax attributable to gross valuation misstatements. No penalty is imposed under that section, however, unless the portion exceeds $5,000. Sec. 6662(e)(2). A gross valuation misstatement denotes any substantial valuation misstatement, as determined underPage: Previous 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 NextLast modified: November 10, 2007