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. Donating Art: Taxation Abstraction The tax rules that govern donating art are complex and confusing. Take a closer look. Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates.