As a general rule, all income “from whatever source derived” is taxable. Some taxpayers, however, fail to report some or even all of their income. Some taxpayers do so because of an oversight or misunderstanding of tax rules; others because they choose not to report their income. Underreported income is particularly problematic with those in cash businesses. The IRS has the authority to reconstruct income when it has not been reported.
The IRS uses various methods of reconstructing income, including:
Bottom line: The IRS’s reconstructed income may be more than a taxpayer’s actual income.
Source: Carol Trescott; T.C. Memo. 2012-321
A business loss that exceeds current income may be carried back against income of prior years and carried forward as a deduction from future income until eliminated.