Capital Gains Tax Estimator Use this calculator to estimate your capital gains tax. You are viewing this website at a small screen resolution which doesn't support calculators. Click here to view this calculator. Share | Related Content The Facts About Income Tax Millions faithfully file their 1040 forms each April. But some things about federal income taxes may surprise you. How Income Taxes Work A quick look at how federal income taxes work. Tax Freedom Day Assess how many days you'll work to pay your federal tax liability.