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. Red Flags for Tax Auditors Here are six flags that may make your tax return prime for an IRS audit. Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates.