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. Do You Owe The AMT? If you want to avoid potential surprises at tax time, it may make sense to know where you stand when it comes to the AMT. Tax Freedom Day Assess how many days you'll work to pay your federal tax liability.