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. Understanding Marginal Income Tax Brackets An inside look at how marginal income tax brackets work. Home Mortgage Deduction Use this calculator to assess the potential benefits of a home mortgage deduction.