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 Comparing Investments This calculator compares the net gain of a taxable investment versus a tax-favored one. Do You Owe The AMT? If you want to avoid potential surprises at tax time, it may make sense to know where you stand when it comes to the AMT. Capital Gains Tax Estimator Use this calculator to estimate your capital gains tax.