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. What Do Your Taxes Pay For? Here's a breakdown of how the federal government spends your tax money. Social Security Taxes Estimate how much of your Social Security benefit may be considered taxable.