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. Tax Reform: Before and After What did the 2017 Tax Cuts and Jobs Act change? Here's a quick snapshot. Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates.