The Facts About Income Tax Millions faithfully file their 1040 forms each April. But some things about federal income taxes may surprise you. Share | Related Content Capital Gains Tax Estimator Use this calculator to estimate your capital gains tax. What If You Get Audited? The chances of an IRS audit aren't that high. And being audited does not necessarily imply that the IRS suspects wrongdoing. Social Security Taxes Estimate how much of your Social Security benefit may be considered taxable.