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. Six Most Overlooked Tax Deductions Six overlooked tax deductions to help manage your tax bill. Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates.