The IRS has increased the number of audits on individual tax returns to 1.3 million in fiscal 2006 from about 618,000 in fiscal 2000. [...] Your odds of being audited go up with your income and the complexity of your return. [...] the agency uses a mathematical formula to identify returns with a higher likelihood of finding more tax due. Most returns -- those with income below $100,000 -- will easily pass this test because they are less complicated. In fact, only 0.89% of those returns were subjected to an audit in 2006, and 82% of those were correspondence audits. For those making more than $100,000 but less than $1 million, about 1.67% of returns were audited, though 56.4% of these were correspondence audits. Odds are less favorable for the wealthy: More than 6% of returns with income of $1 million or more were audited in fiscal 2006, and 54.7% were in person. "If you're earning that kind of money and we notice a problem, you're going to hear from us," IRS Commissioner Mark W. Everson says in a statement on the agency's Web site.