what is the amount of substantial understatement  penalty for tax
Penalty for Substantial Understatement of Taxes. You understate your tax if the tax shown on your return is less than the correct tax. The understatement is substantial if it is more than the larger of 10 percent of the correct tax or $5,000 for individuals. For corporations, the understatement is considered substantial if the tax shown on your return exceeds the lesser of 10 percent (or if greater, $10,000) or $10,000,000.